That really is David Thewlis' penis that we get a glimpse of in a poolside scene. Originally his agent rang up and spoke to writer-director Bernard Rose, saying that he couldn't possibly reveal his penis as he was in the Harry Potter films! Thewlis however disagreed.
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.
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.
Howard Marks: A dealer is really just someone who buys more dope than he can smoke. And I have to say, I'm ashamed, I tried to smoke it all. There was just too fuckin' much of it.