my understanding is that if you continue to drive with your US licence, past the 1 year grace period, your US licence becomes 'invalid' in the eyes of the UK authorities. if, god forbid, you got into a serious motoring accident, your insurance could/would claim that you are driving on an invalid licence and hence not entitled to their cover. so... get the US licence. i fought the whole idea for awhile, i thought it was stupid and arrogant and obnoxious of the brits. but, i'm a better driver for it and i felt so chuffed when i passed. it's like being 17 again. sort of.