Tonight we'll take you ind a radical underground. Home grown terror is top of mind. "Nightline" gained unprecedented access to a movement of young Muslim fundamentalists who want to impose shiria law... See More
Tonight we'll take you ind a radical underground. Home grown terror is top of mind. "Nightline" gained unprecedented access to a movement of young Muslim fundamentalists who want to impose shiria law on the west and the right-wing group that has risen up and essentially declared war. Here is ans's lama Hasan. I just heard that. They just said racist. Reporter: Walking down the street with tommy Robinson is dangerous business. What's he saying now? He is the founder of what many kid to be Britain's biggest hate group. His name has become a symbol for anti-muslim hatred. Why the You bring your camera? In this neighborhood that makes Robinson a marked man. Robinson calls himself a soldier. Oh, god. No, no, no, no. And this is his war. America is going to see firsthand what is going to happen. This is what its happening. This is coming your way. On one side, british born radical muslims. We don't follow presidents or prime ministers. Reporter: Who believe they're fighting a holy war against the west. And want the law to rule. There is no such thing. On the other, the far right movement Robinson founded. He is our one leader. The one and only leader. English defensemen says their mission is to fight radical Islam. What can we do? It is too late. It is never, ever, too late! Reporter: But the edl became synonymous with racism and islamaphobia. Its members connected to hate crimes and mosque bombings. It was tempting to brush the edl aside as racist thugs set fear. But so many ordinary citizens were responding to their message. I had to find out why not only as the a journalist, but as a Muslim woman myself. I have spent maybe all of my life here in London. Four years I have reported from both the middle east. And here at home. This is a very happy moment for both William and Kate. But as I was about to find out, this is the assignment where those world collide. , stab your mum. All death threats people have tweeted you. My journey began in north west London. Just constant threats. Daily. I met the leader of the infamous edl. You , who the Are you saying stuff about muslims. If I see you on the street I will make you bleed. You . He wanted to show me the Muslim area of his hometown. More like an islamic ghetto. Oh, there is plenty to discuss, yes. This is my town. This is where I am born. There is not one English person there. No English shops. Avoid it. This isn't a Muslim shop. A bicycle shop. It is not all islamic shops. I have to say, look, everything that I read has been quite frightened of your group actually. If you listen to what we are saying. I don't want all muslims to leave or hate all muslims. Reporter: Heap does admit there are racists in his group who do. Put it in perspective. 2,000 minimum islamist, terrorists in this country that wish to inflict murder and war on the country. Now my biggest fear is in 20 or 30 years that will be 20,000. A small army. I have a duty as a father and duty as englishman to do anything we can to prevent that. What was the tipping point for you? This is an attack that is genuinely shocked the world. A british soldier attacked and beheaded on the streets of London. The soldier who was stabbed to death. By two knife-wielding Muslim converts. Two killers describe themselves as soldiers of Allah. Reporter: This horrific attack took place. As I reported on this hideous crime. All I could think was not again ate to home grown radicals using my religion as an excuse for unspeakable acts. The blow back was immediate. At the center of it. Tommy Robinson and the edl whose membership skyrocketed. Political Islam. Political Islam spreading across this country. Reporter: As much as I disagree with tactics of the edl I understand tommy Robinson's anger. Because like most muslims I condemn any violence committed in the name of Allah. Yes to shariah. There are extremists among us. I track them down at a rally in east London. We don't shake hands, men and women. Reporter: This is the founder of a radical Muslim group that was banned under Britain's terrorist act. In this video you can see one of lee Rigby's killers over his shoulder. Do you condone killing lee Rigby. You have to look at the wider picture. Look at lee Rigby. If you don't have a minute of silence. You would never speak. Where is your silence for the muslims. Sudden lep I found myself caught between the group and far right counterprotesters. Move back. All of a sudden it is kicked off. We have, I don't know where these guys come from. If he's really getting out of hand. Goknows what is going to happen. This person, has been allowed to walk around our streets. This is an absolute disgrace. Reporter: Rallies are one way chowdry's followers promote shariah. Several have been imprisoned for activities on so-called shariah patrols. It shows the young Muslim men filming themselves confronting non-muslims. Remove yourself away from the mosque. Commanding them to obey islamic laws. Why are you bothering me? Walking through a Muslim area. Awe all harassing people they believe to be gay. You are dirty, mate. Women they kid dressed immodestly. We don't care. It's great Britain. It is not so great Britain. Vigilantes, implementing Islam. We are here to call for an regime change in Britain. One of his proteges. A british born convert. Who frequently leads patrols. Do you do that kind of thing, you do, shariah patrols. We haven't gone on that patrol. I will not contell it. -Up are not. It is none of your business. Of course, as the a Muslim, I am living in society. I see something wrong. He agreed to let me come along on a patrol. I had no idea what to expect. So here we are on the streets of white chapel. Friday night what is it you are hoping to achieve tonight. One of many nights which weave come out and we engage with the community. Tell them about Islam. Part and parcel of the campaign to bring shariah. How far are you willing to go to get shariah law across the world. Would you use violent means? Never know what in the future lies ahead. Reporter: To what extent would you go to to got what you want? Jihadee is not a bad thing. A noble aim. When it is established that will be the beginning of the end of the United States of America. The entire world. Currently governed by man made law. Meanwhile members of the patrol were busy taking down ads for escort services. I am going to ring these people and tell them what they're doing is unacceptable. We are the muslims in white chapel. We do not were to have your business in this area. Fooe female modesty was quite a sore spot. Dupe you've think I should be covered up. I believe every single woman should be covered up. Yes. Are you kidding me? No. How can you say that. I am offended. I think I am dressed modestly. Are you Muslim? Yes. I am surprised. Because the the questions you have been asking me they seem aggressive, very anti-islam, anti-sharia. It is my job to ask. The thing is, look, we shouldn't identify ourselves by our profession. Muslim first. Muslim second. Muslim last. Reporter: I was stunned by what I was hearing. We were in London a few miles from Buckingham pallals. Reminding even more disturbing the effect they have on the youth in the streets. The patrol was urging them to give up any sense of loyalty to their country. You want ideology. The muslims -- Even found a young man who was willing to convert on the spot. I believe. I believe. That nothing. That nothing. Has the right. To be worshipped. Except Allah. Feels good, really. A part of saying.
This transcript has been automatically generated and may not be 100% accurate.