It sounds like something to do with the front wheel sensors as Nick has pointed out which does make a bit of sense as i've just had the sensors out to do the wheel bearings so i am going to check that they have gone back in ok, the manual does acctually say that you should use a new o-ring and lots of grease when replacing the sensors which i didn't do so will have them out again, if theres no difference then i shall replace them.