Full transcript: One-on-one with British Prime Minister Theresa May

— -- CHIEF ANCHOR GEORGE STEPHANOPOULOS: Madam Prime Minister, thank you for doing this. I know you've just met with your counterterror team. What's the latest on what happened today?

PRIME MINISTER THERESA MAY: Yes. Well, we've had another terrorist attack in London on the London Underground. Cowardly attack. And it was a device that was obviously intended to cause significant harm. Twenty-two people were injured, and they're being treated in hospital, not-- obviously our thoughts are with all those who've been affected.

STEPHANOPOULOS: Treating it as an act of terror right now. And President Trump was up and tweeting this morning. He said that those behind this were in the sights of Scotland Yard. Is that true?

MAY: Well, I don't think it's helpful for anyone to speculate on what is an ongoing investigation. The police and the security services are doing the work necessary to discover the full circumstances of this cowardly attack that's taken place, and to identify all those who are responsible. And we-- our threat level remains at severe and I'm pleased to say that our emergency services were on the scene of this attack immediately. And, once again, I admire and thank them for their professionalism and bravery.

STEPHANOPOULOS: And the rest of the city has carried on, but you've said in the wake of these other attacks, "Enough is enough. Things need to change. It's time for some even embarrassing conversations." What did you mean by that?

MAY: Well, it is necessary for us to look, as we are doing, at whether our police and security services have the full capabilities, the powers that they need. Of course we review after any incident that takes place, and we have had, sadly, a number of terrorist attacks in the U.K. this year--

STEPHANOPOULOS: Do they have the powers they need?

MAY: Well, the-- the exercise is being done. I've given them extra powers over my time in office, particularly when I was home secretary before I became prime minister. I've given them extra powers. But we look again. But one of the issues that we really need to be addressing, and I'll be raising this when I'm at the United Nations, is the question of the use of the internet by terrorists for terrorist planning. But also this using it for the spread of extremism, of hatred, of propaganda that can incite and can inspire terrorism.

STEPHANOPOULOS: Are you gonna need companies like Facebook and Google to do more?

MAY: We're talking to them about doing more. And indeed companies have come together. They formed a global forum to look at what they can do to be dealing with this more quickly and in a better way than they do at the moment. So we're working with the companies.

STEPHANOPOULOS: President Trump also tweeted this morning that the solution is a bigger, tougher travel ban. That's an idea you've been against. Is it something you would reconsider?

MAY: I think what is important is that we're able to have the powers to look into people, to identify people who may be wanting to cause us harm and are plotting to cause us harm. And to be able to take the necessary action when people do cause us harm. As it happens, here in the United Kingdom when I was home secretary I banned more extremist hate preachers. I excluded more extremist hate preachers from coming to THE U.K. than any home secretary before.

STEPHANOPOULOS: As you mentioned, you're coming to the United States this week. You're speaking to the United Nations. You're relatively unknown to most Americans. What's the most important thing you want them to know about what you're trying to achieve?

MAY: Well, what I'm-- there are two things-- that I'm particularly going to be look-- talking about and dealing with when I come to the United Nations. One is this issue of ensuring that we can stop terrorists from plotting online, plotting on the internet, and that we can stop the spread of the hateful extremist ideology, which can inspire terrorism. I think that's really important for us.And another issue I'm going to be talking about is something that most people probably don't think about, don't think happens. It's what incredible all modern slavery, which is when people are being effectively taken into servitude, into slavery, for sexual exploitation or labor exploitation. It's happening under our noses.

STEPHANOPOULOS: You've been prime minister for little over a year right now. Came in after the Brexit vote. Became prime minister even though you were against Brexit. So were you wrong about that?

MAY: I was-- what I said at the time, before the referendum vote was taken, was that on balance I thought it was right to remain in, but the sky wouldn't fall in if we left the European Union.

STEPHANOPOULOS: But now you have to make it happen.

MAY: Now I'm-- now I'm making it happen. That's right. And obviously we're in the negotiations. But now I think we must take the opportunities that come from Brexit. Some people look at Brexit and think that it was about the U.K. turning inward. It wasn't. It's about us actually looking out around the rest of the world, but ensuring we can control our own laws, our money and our borders.

STEPHANOPOULOS: A lot of other people look at it and say, "It's never gonna happen."

MAY: It will happen. We're in the negotiations. The-- and-- and we're looking at the deal that we can do, the-- the-- the way that we can come to an agreement with the the E.U. for the future, for our future relationship in trading terms. But what this enables us to do is actually-- by having our own control is do our own trade deals. Hence we're talking to the United States, and President Trump is very enthusiastic about a trade deal with-- between the U.K. and the U.S., and I am too.

STEPHANOPOULOS: It has taken its toll on your government. You almost lost the prime ministership back in June. And the former conservative minister, now newspaper editor, George Osborne, has said you're a “dead woman walking,” that passing Brexit would be basically your last act. Your response?

MAY: My-- I'm going to pass Brexit, I'm going to make sure that Brexit happens because the British people voted for it. And I think it's really important that politicians actually do respond and do listen to people. We gave the public the choice. They made their choice. And that's why I think it's important--

GEORGE STEPHANOPOULOS: And after that--

MAY: --for us to deliver on it--

STEPHANOPOULOS: --you'll still be prime pri-- prime minister?

MAY: Well, the next election isn't going to be until after-- we have the-- Brexit. Until after we withdraw from the European Union. I've s-- as-- I've said, the-- this-- a long-term challenge-- long-term challenges for the U.K. Some of those issues I'll be addressing at the United Nations. I'll also be addressing them in Canada before I go to -- and go -- and I'll be meeting Justin Trudeau and talking to him about issues like the terrorist use of the internet. These are challenges for us all.

STEPHANOPOULOS: You were the first foreign leader to meet with President Trump. How do you get on with him?

MAY: I do get on with him. And of course, as you know, President Trump has-- actually has an affection for the United Kingdom. Like many Americans he has family connections with the United Kingdom, and we work very well together. And we work-- most recently, this is-- we've been working on the issue of Hurricane Irma.The U.K. and the U.S. have always had a special relationship and worked well together. An-- and-- I'm-- would like to say thank you to the United States for the help that they've given us in relat-- in relation to the response to Hurricane Irma. We've been able to help the French and the United States have helped us. It's an international effort after what has been a devastating hurricane.

STEPHANOPOULOS: You say that President Trump has affection for England. It doesn't appear that the British people have much affection for him. I saw a recent poll in June. Only 22 percent of the British people have confidence in him to do the right thing for the world. What do you say to your fellow Britishers?

MAY: Well, what I say is that they should see what President Trump has done. I mean let me give you one example-- because I know a number of people were concerned before he became president about his statements about America's commitment to NATO. NATO has been the bedrock of Europe security. I was very pleased when I came over to see him, shortly after his inauguration, that he gave an absolute 100 percent commitment to NATO. America continues to stand by us in-- in supporting that security and ensuring that security of Europe.

STEPHANOPOULOS: You've also got the travel ban. His comments after Charlottesville. Pulling out of the Paris Climate Change Agreement. Big differences.

MAY: Well, I think the point about the special relationship between the U.K. and the U.S. is that when we do disagree we're able to say so. And-- pretty bluntly. And I'm-- for example, on the Paris issue that you talk about, the Paris Climate Change Agreement, I've made very clear I was dismayed when America decided to pull out of that. And I-- as I've said to President Trump, I hope that they'll be able-- able to find a way for America to come back into the agreement.

STEPHANOPOULOS: Do you still think he'll be able to come here for a state visit or is that just not gonna happen?

MAY: No, Her Majesty the Queen-- issued the invitation. The president has accepted it. It's just a question of getting dates to-- and sorting out the logistics.

STEPHANOPOULOS: So it has nothing to do with the opposition here in the United Kingdom?

MAY: No, this is-- this is about finding dates when-- the invitation was issued and the invitation has been accepted.

STEPHANOPOULOS: Another missile test from North Korea just yesterday. Are we gonna have to just learn to live with the idea that North Korea's gonna have nuclear weapons forever?

MAY: Well, I think what we need now and-- is a-- reinforced, and what we're seeing is a reinforced international effort to put pressure on North Korea-- to stop-- look, what we have seen in recent weeks, and indeed before that, is continuing provocation from North Korea with illegal actions. These are illegal tests that they're taking out-- carrying out. I think it's significant that we saw at the United Nations Security Council that unity of everybody coming-- together around the table, including Russia and China-- and agreeing to the stricter sanctions that have recently been agreed--

STEPHANOPOULOS: But these are still--

MAY: --by the U.N. Security Council.

STEPHANOPOULOS: --baby steps, aren't they?

MAY: These are important. These are important steps. So continuing to put pressure on North Korea to stop what is illegal activity.

STEPHANOPOULOS: Can Kim Jong-un, though, be deterred? Is this a man who can have that kind of rational calculation?

MAY: Well, I think it's for the international community to work together to ensure that we do deter him. I think it is important that we act-- first of all, that we act together, and that we do what is necessary to deter him. I think it's very good that the United Nations Security Council has come together and shown that unity, not just in words but actually in a resolution that puts into action sanctions that will have an impact.

STEPHANOPOULOS: I wanna switch topics to Russia now. There are reports that British intelligence were the first to tip off U.S. intelligence to the idea that Russia was interfering in the United States election. What can you tell us about that, and what can be done about it?

MAY: Yeah. Well, I think you'll find that-- that we've been very clear-- that the-- it was reference to I think something that had come from somebody who was no longer employed by the British Intelligence Services. But look, the issue of-- of Russia and what Russia is doing is another area that we need to be wary of and to watch very clear-- clearly and carefully.We're very clear in the United Kingdom about the illegal annexation of Crimea, for example. We need to ensure that we're s-- we see what is called the Minsk Agreement, which is an agreement in relation to Russia and the Ukraine, put fully into force so that we're able to give Russia a very clear message that you can't just walk into somebody else's territory--

STEPHANOPOULOS: But he's--

MAY: --in the way they did.

STEPHANOPOULOS: Yeah, he-- that's what he's done in the Ukraine. Russia's also interfered in the French elections. Interfered in the German elections. Do you think they interfered in the Brexit election as well?

MAY: I-- is-- there's no sign of that. But the point that you make about interfering in elections is a very important one, and a very clear message should go that no country should be interfering in another country's elections. These elections should be free and fair. The view of the people.

STEPHANOPOULOS: Can the West work with Putin?

MAY: Well, the West is work-- working with Putin. I mean the United States and Russia, obviously, are trying to find solutions in relation to Syria, another area of the world where we all need to work to find a solution that is going to stop the terrible scenes that we've seen in Syria, but also of course Syria is-- stop Syria being somewhere where Daesh, where the terrorists, can be and can be causing harm to us in the rest of the world.

STEPHANOPOULOS: But do you think he's a reliable partner there?

MAY: Well, I think what is important is that engagement takes place in the interests of the region and the interests of the world.

STEPHANOPOULOS: Hillary Clinton has a new book out this week, looking back at the election. It's called What Happened. Quite candid in many places. And one of the things she talks about is being a woman in politics. She says it's not easy. In her own words, she says it's excruciating and can be humiliating. Do you identify with that?

MAY: Look, I've-- I've always approached my-- being in politics in a very simple way, and think-- not think about that I'm a woman in politics in the sense of-- of how I'm being treated by others, but just get on with the job that I'm doing. And that's what-- that's what I do.

STEPHANOPOULOS: You know, we were getting a little tour of this-- of 10 Downing Street before you came in, and we're told that Margaret Thatcher left a little mark up in the corner of-- of that door. A little Thatcher there. What mark do you intend (LAUGH) to leave on 10 Downing Street?

MAY: Well, I-- I'm-- I'm-- I'm not sure I'm going to go 'round-- (LAUGHTER) destroying the furniture or the walls with putting marks in or anything like that. Look, I just-- I-- I'm here as prime minister. I'm getting on with the job, dealing with the challenges that we face here in the United Kingdom.Some of those are challenges that we face like ensuring we get Brexit right, but actually there are other challenges, which is shared across the world, dealing with terrorism. Dealing with modern slavery. Ensuring we have free trade around the world that brings prosperity and jobs to people. Those are the challenges we're facing.

STEPHANOPOULOS: Thank you for your time today.

MAY: Thank you.