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Almost certainly brake pads sticking to discs. If you immediately inspect the discs you'll see evidence. They'll soon shine up after some driving and testing the brakes - Good idea to always test your brakes at the start of any journey.
I had the worst case ever yesterday and had to really mount the revs to free it. For this reason I have been leaving the handbrake off in my garage and just using P, but it obviously doesn't solve the problem.
The other thing to watch is if you use the brakes hard and a lot such as on a track day, don't put your handbrake on until your discs have cooled down.
Question to all:
Does P action the pads onto the disc?