I suspected the rear pads were due to be changed and found the rotors were rusty, driver side more than the passenger side. there was still some meat left on the old pads but changed them anyway and checked the caliper pistons which seemed OK. Also the handbrake hasn't worked since I got the car so tightened the cables. The handbrake now has resistance but doesn't hold the car. Where do i start?

That sounds pretty serious...could be corroded pistons stuck in the caliper bore, caliper slides rusted solid, blocked flexible hose to rear brakes etc. Unless you have a fair idea of what could be wrong and are familiar with brake components I'd take it to a brake place which will cost, but then safety must come first.

Edit.....you say the rotors were rusty - I take that to mean the pads have not been in contact with the rotor surface which is why I say it is serious.

Yeah, just had them apart again and I can't find the problem, so it's off to a brake specialist we go...