I'm not going to spout too much about this lens - if you're seriously considering it, you'll know how amazing and *painfully* sharp this lens is.
I bought mine a while back from Jessops for about £800, but this is now the cheapest it has ever been (by about £50) according to Camera Price Buster, link here: http://camerapricebuster.co.uk/prod196.html
Hope this helps!
EDIT: +3% cashback through QuidCo :-)
This really is an *amazing* price for a top notch lens, and if I didn't already own one, I'd buy one in an instant!