Cheers mate, having you describe that reminds me that I have actually done it!
I found that one of the o-rings on the pivot was the wrong size (too big) and was squashing when tightened, hence the gripping of the lever.
Having checked the spares manual, the o-rings should be the same size on both sides (same part number) so I replace the larger one with the right size o-ring from a pack I'd bought in B&Q for 99p to fix something else - probably a leaky tap or something.
Anyway, job done. Doesn't mean I use the back brake though
