Belkin 12V DC to 220/240V AC Inverter is available from Morgan Computers for £15.26 inc VAT
They offer a FREE in-store collection at London (or other showrooms) but if you prefer home delivery, then the price is £19.96 delivered. Go through QUidco for 2% cashback.
Description: Power your notebook, digital camera etc from your car cigarette lighter. 140W AC/DC power inverter (converts 12V DC to 220/240V AC). Provides a standard 3 pin plug socket from your car cigarette lighter. Suitable for a notebook, camcorder, digital camera, portable DVD etc. Power LED indicator, overload protection and replaceable fuse. Brand new & Two year Belkin warranty