How do I remove centre tail light cover?

[plantchick]

Preferably without destroying anything.

I feel a right twit asking, but I've searched and searched and can't find anything on it.

The left hand side is sticking out enough to be (at least one) source of a boot leak. I can see the plastic thingies that look like they should fit snug beneath the trim, but either its jammed on the right or I just can't work it out. I'm scared to use too much force because of the electrics.

Can anyone tell me how to remove it?