tailgate lock stuck

This is to ask if anyone has any suggestions as to how to unstick the tailgate lock? I have squirted with WD40 but no luck yet.It has only happened once before and it just opened again after driving round for a bit.It is locked as part of the central locking but I have tried using the key as well.Any ideas? Thanks,Mary.

Is it fair to assume that it's T5 based? It's not completely impossible that it's T4 based - though a bit unlikely.

If so, there are several possibilities, but firstly, is the external lock in the correct orientation (as shown in the owner's handbook - note that the correct position is not obvious) for manual opening? Secondly, will it open from the internal release, with the internal safety button up?

If neither of those causes it to yield, probably the most likely reasons are either that something has been dropped into the recess where the latch is, or one of the operating rods inside the tailgate has become unshipped.

Yes it is a T5.I have tried all the options you suggested but still no luck.When it stuck it was because I left it partially open and went into the van and it closed by itself at which point it locked even though the van was unlocked. I am thinking it has not properly engaged the lock so we are going to try taking it for a short bumpy ride today! Any other ideas would be helpful.Thanks,Mary.

It depends how it's not opening. If you can feel the mechanism engaging as you pull the handle then I would suggest that someone gets inside while the handle is pulled and gives the tailgate a firm push.

If there is no feeling of engagement at the handle with the key in any position then I would suspect a linkage problem, more than something jammed in it. If so, it's probably going to be a horrible one to resolve on a Trident (or a Trooper, for that matter).