Ah forgot, as I joined the start of the M1 on the way home the engine management light came on
Pulled onto the hard shoulder & got the OB2 palm out of the glove box, turned out to be " Fuel sensor rich 2nd bank "
Did a reset and all was fine, that's the second time I've had that code although the last time was over a year ago, it's never when the engine is either cold or hot. It must be a few miles from the ace to the M1 and the last time was when I had nearly got to the M1 from the Caldecote Arms in MK
May be it's allergic to the M1