Thanks for the response, the latch mechanism was the first thing I tried and it works fine; latched with my finger then unlatched it with the badge handle - no problem there. I have noticed that the LH side of the tailgate sits slightly proud down by the left-side tail light, the RH side not so much. I tried sitting in the boot and closing the tailgate from the inside to see if anything was apparent but couldn't see anything obvious. It just seems bizarre that it happened overnight. Looks like it might be a job for the service department. It's a total pain because the car is effectively unlocked at all times right now.