Found this on eBay. NO idea if it is any good, but my luck with corded inverters like this is better than the name-brand one-piece/no wires units. It has a USB output (kind of where the switch should be). US$5.99, + US$8.99 S&H (world wide?). About £7.50 total? eBay item #330228717994.
Seller is "bestselling888". (trivia- 8 is lucky in Asia, the Beijing Olympics open on 8/8/08)
Anyone who knows about that inverter should speak up!
Might be worth a look, given the prices of UK RE stuff. G-