I found this whilst looking for something else, seems like a good deal, it's less than half what Ebuyer charges! (£23.45).
You may not need one now but it's worth keeping one in the boot of the car just incase you need to power something that runs from the mains... Phone charger, laptop, 50" LCD TV?
Belkin AC Anywhere 300W DC/AC Power Inverter - Portable
Running out of power is an event of the past with AC Anywhere. The unit simply plugs into any standard, 12-volt DC vehicle cigarette lighter socket to convert your vehicle's battery power to 230-volt AC (common household current). Now you can keep laptop computers, PDAs, and AC appliances powered and operational wherever you go.
Powers and recharges portable devices using 300-Watt power inverter
Converts DC Power to AC power from a cigarette lighter socket
Fits all standard car cigarette lighter jacks
Works with laptop computers, portable printers, small TVs, CD Players, and other portable devices
Converts 12 volts DC power to 230 volts AC power
Automatic overheat shut-off at 66 Celsius
Power LED indicator
Child safety shutters
Replaceable fuse included
Belkin 2-Year Warranty
Device Type DC to AC power inverter - external
Localisation United Kingdom
Input Voltage 12 V
Output Voltage AC 230 V ( 50 Hz )
Power Provided 300 Watt
Output Connector(s) 1
Manufacturer Warranty 2 years warranty