Canon EF 70-200mm f/2.8L IS II USM Telephoto Zoom Lens $1974 at B+H

[smirkypants]

Or why not fly to the US and buy it, and have a holiday into the bargain ?

You can often find flights from london to new york (or newark, new jersey) for around $500-$600 for a Thursday to Tuesday trip. You can get a cheap/decent hotel on hotwire.com for around $100/night more or less, depending on how much you're willing to slum it. Pick an area close to Adorama and you're in like Flynn.

You don't save any money, but it's essentially a free trip!