Thanks for all the tips guys. I like the process of elimination with the spark plugs too Blacky. Sounds like a sensible place to start if that van isn't running smoothly.
Fortunately when I started the engine the following morning before I set off to Wales the wobblyness had disappeared, so the run the night before for the first time in a few weeks had presumably given it the shakedown it needed and got it running a bit smoother again. That would be in line with your theories.
Something else that sprung to mind was that I had the van jacked up on one side for a few days with one of the wheels off. Would that cause the engine mounts to squash down on one side more than the other and take a while to settle back down again? I have noticed before that the van tends to lean a little to one side if I have had it jacked up for a while and takes a little while to even out again. Just a thought.
PS. Had a lovely trip to the Pembrokeshire coast in Wales too. Lovely coastline. The friends who came with had fun taking down the tent in a storm though
Tim.