It isn't always the case that The Simpsons is cut by Fox before it reaches the UK broadcasters - several parts have been kept in for earlier broadcasts have been removed of late (such as "This is the line to register as a sex offender", which was intact for many Sky One showings), several parts which were once verboten since reinstated ("oh crap! I certainly shouldn't have admitted he was a customer"), and some parts that have been given a single fleeting showing in the UK (such as the bombing of 'John Bull's Fish & Chip Shop' on St Patrick's Day in the episode "Homer vs. the Eighteenth Amendment", kept in on a BBC2 evening screening, and not shown in the UK since).
Some of the stupidest editing was certainly done by Sky One after the death of Diana, in the episode "Rosebud", where Monty Burns' exclamation "Damn you, Paparazzo!" saw the word 'paparazzo' blanked out. The episode was left this way for a good couple of years, before it was reinstated.