[InOne]

A Streetcar Named Marge (8F18)
This episode only aired once on BBC 2. It is not known why, but it's probably due to the offensive "New Orleans" song. Channel 4 came under fire in 2005 when it aired the episode shortly after Hurricane Katrina devastated New Orleans. They ran an apology two days later and have subsequently cut the song from the episode.

The City of New York Vs. Homer Simpson (4F22)
This episode was due to air on BBC2 in late 2001, but because of the 9/11 attacks it was pulled, as it was in the U.S. and other countries, since it features the Twin Towers prominently. BBC2 never aired it in the time they had the rights, and it wasn't until 7th August 2005 that Sky One finally plucked up the courage to show it... with extensive cuts (which we find grossly disrespectful).

The Cartridge Family (5F01)
This was banned by Sky One for constant foolishness with guns. It was released on a VHS compilation, Too Hot For TV, so that British viewers could see it if they wanted to. The episode was first broadcast in the UK when it made it onto the BBC, on 26th October 2001. When the rights returned to Sky they finally aired it, on 26th September 2005.

Natural Born Kissers (5F18)
There was a rather large debate in 1999 whether to air this episode or not. Sky held it over and allowed it to be the premiere of Season 10. This was about the point they stopped cutting as much in newer episodes.

Wild Barts Can't Be Broken (AABF07)
In October 2002, when the Washington Sniper incident was taking place in America, this episode was postponed on BBC 2 because of Moe's line, "That sniper at the all-star was a blessing in disguise," and Wiggum's "any child found outside after dark will be shot!". Eventually after Thirty Minutes Over Toyko had aired, this episode aired, but with the two Sniper lines cut, prompting the question: why didn't they do that in the first place? The lines were later reinstated.

Day of the Jackanapes (CABF10)
During 2002-2004 this episode was dropped from Sky One's schedules. The reasons are unknown, but the most likely explanation is because it features Bart as a suicide bomber. It was in this same period that The City of New York Vs. Homer Simpson was banned (see above) due to the 9/11 attacks.

Weekend at Burnsie's (DABF11)
The plot features heavy drug use, which gave it a TV-14 rating in the U.S. Sky One refuse to air this before the watershed, though when it is on it is uncut. Unfortunately, this means it airs very rarely because there are no regular post-watershed slots for the show.

Love, Springfield Style
This episode has been held back due to the repeated use of the word "bollocks". It will air in a late-night slot amongst Season 20 episodes.

'Banned' possibly might be a bit strong but it gives you the reasons why they're not shown. It's quite an interesting site, shows you all the edits made to the episodes so they're allowed to air. http://www.simpsoncrazy.com/ukcuts