When I shut the boot, it pops back open, not enough for the boot to open fully however, and you can't open it by pushing the button above the number plate. You have to unlock it again from the remote.......

There are no obstructions around the lock or the clasp and it only happens every now and again??

Could be a faulty locking mechanism I had mine replaced under warranty and I just picked my brothers vrs after getting a replacement rear wiper motor and boot release mechanism the car is only 6 months old. Both ours are hatchbacks though so I'm not sure if the locking mechanism is different. Failing that the clasp may just need adjusted