How can I pitch Fiasco to a UK audience?

Show them this review by Quinns and Paul (British board game reviewers): http://www.shutupshow.com/post/20406644151/review-fiasco

It's a game about people whose ambition exceeds their common sense, and they invariably get themselves into trouble by crossing certain lines. Greed, lust, and other sins are always involved. It is usually funny but sometimes it is sad.

I think the Guy Ritchie route is a good one. Lock, Stock and Two Smoking Barrels is a note-perfect Fiasco.

Do your kinsmen like Tarantino? Jackie Brown = perfect.

Have you looked at the filmography on page 124? The Bank Job is a UK-themed Fiasco. In Bruges is about English fools in ... Bruges.

One way would be to frame them in the movies of Guy Ritchie Both Lock, Stock and Snatch were very high-grossing films in the UK. The essence of the capers is that they're Crime Comedies focusing on (TV Tropes warning) A Simple Plan - TVTropes.

Fiasco doesn't need pop-culture references to describe it.

One way of describing it: A bunch of desperate criminals, all working at odds with each other decide to ask the universe: "What could possibly go wrong?" And the universe... answers.

Refer them to this game summary.

Looking at the quote you mentioned:

You’ll play ordinary people with powerful ambition and poor impulse control. There will be big dreams and flawed execution. It won’t go well for them, to put it mildly, and in the end it will probably collapse into a glorious heap of jealousy, murder, and recrimination. Lives and reputations will be lost, painful wisdom will be gained, and if you are really lucky, your guy just might end up back where he started.

poor impulse control = "they keep stuffing up their own plans because they're stupid, greedy, and the universe is taking the piss."

Here's a potentially reworded pitch:

You've got a plan. It's a simple plan. It'll set you up after those long hard years in [Really horrible English Suburban city] behind the counter. It's perfect. Nothing could possibly go wrong. Of course, there's one slight flaw, you need some help with the plan, and your friend's... not quite perfect. Not like you, anyways. Then... then things turn into one of those days where nothing goes right, and it's easier to say "Bugger this for a lark." But you can't. It was the one time when things couldn't be stuffed up, but they were. At least you're not alone, and you can revel in the fact that your friends' perfect plans have also gone "belly" up. (replace with correct word) Sometimes, all you can do is laugh -- not that laughing will do any good, mind you.