It is possible that your car has the "Auto-lock/unlock" feature and it is active. You can disable the feature outlined
<<HERE>>. This feature unlocks the doors when you shut the car off and open the doors. If you are able to disable the feature, and the problem seems solved, you have an issue related to that system, possibly wiring related or BCM issue. There is possibly a recall issue in the US related to the latch switch, however Canadian cars arent included or dont experience the same problem, you may or may not have a case in the UK.