I watched this Simpson's episode last night when all the family come to London. It was very funny in places. Bart and Lisa having British candy, flipping and re-enacting the opening scenes from Trainspotting complete with Iggy Pop and spinning Maggie's head as in Renton's cold turkey, Tony Blair was interesting in his cameo "I've just met Mr Bean", Homer "rear-ending the Queen" and only getting off when he promises to take Madonna back to America, the Judi Dench diner.
All in all I think we got off lightly compared to other Simpsons episode where they go away. Australia and Japan spring to mind.