There is indeed a UK Marriott Visa. It's issued by Halifax, there is no annual fee, you get 10,000 Marriott Reward points on first use, and it gives you 10 nights towards status each year (enough for Silver).

I believe you get something like 1 MR point for every £1 you spend (which is equivalent to about 0.6 MR points per $), or 2 MR points per every £1 spent at Marriotts - a very poor earning rate, so while it seems to be worth having, it's probably not actually worth using it.

Link for more info: http://www.halifax.co.uk/creditcards/marriott.asp