I put my watch back an hour before bedtime, also the alarm clock - good thinking eh?
Woke up at around 5am with my watch showing the correct (GMT) time, and the alarm clock showing 4am.
Turns out that although the alarm clock isn't synchronised by the atomic time signal, it does adjust for BST and GMT all by its annoying little self!
As for the car clock, I did manage to adjust that without needing to consult the 600 page manual (I kid you not), although I confess that during the process I inadvertently changed the language to Danish and rescanned all the DAB channels!