According to Christopher Morris, Barry, the Jihadist group leader, was based on a former BNP member who in an attempt to out-knowledge the Asian youths he regularly assaulted, studied the Qur'an and as a result "accidentally converted himself" and became a Muslim.
Following Omar's bomb speech in his living room, you can hear Waj shout "fuck mini babybels". According to an interview with Kayvan Novak, this was completely improvised.
The film had its world premiere at Sundance on January 23rd, 2010. The same day, the UK "terror threat" level was raised to "severe" due to non-specific "chatter".
Look for "If you're reading this, find out what's wrong with you" in the small printed credits. As of October 2010, the poster is available in high resolution on the official UK website.
On the UK DVD, wait in the deleted scenes menu until the seagull appears and then press enter. This will take you to a further menu featuring more bonus materials.