It then got worse and I couldn't leave the ignition on at all after turning the engine off without causing it problems unless I left it for a while and then started it.
Now in the mornings when I come to start it wont turn over properly, but If hold the key in the starting position the starter motor starts to build up momentum and eventually starts the car, it sounds like a steam train building up speed!!
I had the battery checked by Halfords and it had 60% life, but it did show up an anonymous error normally related to an earth leak apparently. So I think it must be the starter solenoid that isn't charging properly.
Anyone seen this before?