YAJ update:-
I have been blatting about in the old thing a bit ("Well, the handbrake was working this morning, Officer"). My mech has been off work ill, but is back in action as of tomorrow. He says in an email:
"I will be bringing my special tools with me, and if the calipers are O.K. and I
can, I will rebuild them there and get the handbrake working. You'll understand
more when you see them, but there is a small wedge in the back
that gets knocked out if the calipers don't self-adjust and then you
have to strip them to put it back in. It is a tricky job even when on a
bench and is almost impossible on the car.
The wedge gets trapped in the boot at the back with the grease so
generally you don't lose it unless the gaiter is split open or missing and both yours looked O.K. last time."
He adds that garages often get stumped as they do not have the special tool for stripping calipers and may incorrectly advise fitting new ones, only to find that locating new ones is a mare.