It only went and bloody well done it again on the way home, luckily I was 100 yards from my road so switched off and back on quickly, got to my road it done it again when slowing down, off/on quickly, turn in road and does it again!
Took the unit out again and wiped everything down with a dry tissue, opened it up to reveal the metal brushes and fiddled with them, put it back together and it worked fine on the 15mile round trip to my mums this evening.
Going to ring up the VW/Ford/Seat dealers around here tomorrow to see if they have the unit in stock.