Scrap that, i've found one.
£16 for a bacon cheeseburger.
I get a bit sick of moaning about prices for things like this- I'm fully aware that I sound like a broken record, but seriously, how have they got the gumption to charge that?
Do a search on London's best burgers and Time Out comes back with the top 15. The only ones over a tenner and around £16 are from a Neil Rankin restaurant and at the Mandarin Oriental.