Cheers Nick,
I'll have a look at the rear clusters, as you say they do have a bad reputation. I just though it was all too much of a coincidence and the lights are out rather than dimmed like you sometimes get when a bad earth makes them flash in time to the indicators. The indicator panel sometimes shows both brake lights as being intermittently faulty during a journey, warning goes out when you press the pedal, comes back on when you take it off and look ok when I get out have a look!

The light dipped beam that works is the LHS, the one that has the problem is the RHS, though both of them seem to have local earths and I cleaned and greased the RHS to no avail

CheeRS,
Iain