Yep. Been there had that happen, Vectra handbrakes used to be terrible for this. Was on a hill in a traffic jam once with the van on the back (and the van only weighed 1000kg) and the handbrake just wouldn;t hold it, and that was on a one year old car. Imagine the fun hill starting it.
Much more recently (last year) a colleague parked his 06 reg vectra, got out only to see the car roll backwards down a hill and into a lorry. Had to have a complete mew back end.