Why UK Officials Believe Terrorism Threat in Britain Is Greater Than Ever Before

— -- In perhaps her most stark message yet, British Home Secretary Theresa May warned that Britain is facing its greatest terrorism threat in its history.

"When the security and intelligence agencies tell us that the threat we face is now more dangerous than at any time before or since 9/11, we should take notice," May said today during a news conference in which she was laying out plans on the government's new counter-terrorism and security bill set to be introduced this week.

The home secretary also addressed the serious threat from ISIS, also known as ISIL or the Islamic State, saying the "threat from ISIL has made no secret of their desire to bring death and destruction to the U.K., U.S. and other Western countries."

The new bill, introduced last week and touted as being tough, will be brought forward in order to try to stamp out home-grown extremism. It includes a set of new measures to prevent radicalization, making conditions difficult for extremists to operate, giving the government greater power to disrupt those wanting to travel abroad to countries such as Iraq and Syria to fight.

Since the attacks on July 7, 2005, about 40 terrorists plots against British targets have been disrupted by the police and intelligence services, May said.

"There have been attempts to conduct marauding Mumbai style gun attacks on our streets, blow up the London Stock Exchange, bring down airliners, assassinate a British ambassador and murder service members of our armed forces," she said. "Almost all of these attacks have been prevented by the first class men and women of our security and intelligence services, the police and our allies overseas."

The U.K.'s threat level was raised in August due to the threats from fighters returning from the conflicts in Iraq and Syria. The threat level was raised from "substantial" to "severe," meaning an attack on home soil is highly likely.

The message from May today was clear: The country is engaged in a struggle that is being fought on many fronts and one that will go on for many years. She ended her speech on a sober note, saying, "The threat we face right now is perhaps greater than it ever has been -- we must have the powers we need to defend ourselves."