Throughout the film, there are several occasions when modern UPVC windows are visible - most clearly when the projector is stolen from the school, and in the accountant's office before he gets arrested.
When Howard visits the airport of Shanon for the first time an ATC radar appears on the screen for couple of seconds. It is most likely a Marconi PSR system co-mounted with a MSSR radar which is too modern for the late 70s or early 80s.
The car that Rhys Ifans (Mr Nice) uses during the scene where the police pull his vehicle apart clearly uses a number plate font that was not introduced in Britain until 2001. Prior to this letters had more width and the same hight as the current standard.