I honestly don't know too much about it. When I was at uni, I went to a few seminars where they talked about different concepts within Islam (like the role of women in the religion), but, honestly, I just attended for the free pizza.
I have many friends who are Muslim, but none of them follow it strictly. They believe in their god and whatnot, but they didn't pray regularly, would drink alcohol, ate during the day during Ramadan, etc. I think this attitude is quite common of second and third generation Muslims in the UK - particularly in the middle class.
As for Islamic extremism, I hold two beliefs that are usually held by people on opposite sides of the argument:
1) You cannot say ISIS is not Islam, or that these people are not Muslim. You cannot say "no true Muslim will not do x, y, or z" when people who are Muslim do those things, and many other Muslims agree with those actions. This falls into the "No true Scotsman" fallacy.
Scottish person 1 - "No true Scotsman will put sugar on their porridge"
Scottish person 2 - "But I do"
Scottish person 1 - "Yes, but you are not a TRUE Scotsman".
2) Muslim people do not have any moral obligation to condemn Islamic Terrorism. This is something I see all the time from the "right" on this issue. Whenever there's a terrorist attack, there's an outpour of commenters on Breitbart and the like decrying all Muslims for not condemning these actions.
No sane person expects me to condemn the actions of a person because they're atheist, or straight, or white, or male. Just because somebody shares some characteristic with me, doesn't mean I have any moral connection to them.
When a white guy makes it rich, I don't get a piece of that. So I don't share their problems, either. It's the same with Muslims.