In the real story, it was not Neil, Ivan's brother who told Bono that his brother would not join the band The Hype (later known as U2). Adam Clayton, U2's bass player, called Ivan and told him that he was too young for a gig they would play in a pub so he was out of the band. Curious enough, Ivan is only one year younger than Larry Mullen Jr, the drummer of U2.
While Robert Sheehan's character in this film didn't get the chance to be part of U2, his character in the TV show Misfits (2009) managed to impersonate Bono, insulting him while doing so.
When Neil & Ivan first arrive in London it is the early 1980's yet a taxi can be seen being driven on the other side of the road with the registration plate "L" which was not issued until 1993.
At the bands first practice (in 1976) Ivan McCormick suggests playing a song by Dire Straits. Dire Straits recorded their first album in 1978, so none of them would have known any songs by Dire Straits, let alone have even heard of them.
When Neil is about to leave the garage about discussing the bands future his collar is down. There is a cut in the shot and his collar is up. There is yet another shot from outside of the garage and his collar is down again.
Karl: A word to the wise from an old man before you go. Remember only this: the measure of a man is what's left when fame falls away... oh, and another thing: get as much sex as you can!