Upper tailgate switch sticking

The upper tailgate switch on my 2007 Disco3 sticks. A good thump usually encourages it but it's bruising my hand!! Can anyone advise what the fix is for this problem? I just know it's going to fail completely, soon, and then it's going to be necessary to damage the trim to get into it from inside the luggage space. Help please?

Trim off and a modified switch or actuator

Thanks Stuart. Arranged to get this done - off to Adventure 4x4 next week! Hope it doesn't cost an arm and leg.