Did it this morning by mistake, ( I know...) doing about 30mph round a small country lane, reached for the keys to stop them clunking around, went over a large bump, hand slipped on to the handbrake switch...

And I'm pleased to inform you the car didn't lurch to a halt. It looks like the fact that I had my foot on the accelerator means that the car decided to beep at me and throw up an error rather than apply the handbrake;

"Handbrake fault, please see owners manual"

A yellow brake warning light popped up on the dash. I stopped a bit later down the road in a lay-by. Pressing the handbrake button a couple of times seems to clear the error, and it all starts working again.

The moral of the story? If something rattles/clunks leave it be, it's far less stressfull...