Rear brake caliper sticking?

Just a quick post to say it's fixed

Took the caliper apart again and refitted the piston, everything looked ok. Yet the problem disappeared when reattaching it, maybe an uneven piston?

Either way that sorted out what was left of the binding problem.
The reason the rear wheel wasn't spinning freely, a dry chain with tight spots.
After lubricating the chain thoroughly & again once the chain was warm, the bike is sweet as a nut !
Obviously need to look at a new chain and sprocket set in the very near future.

Thanks for the help everyone, got there in the end

[aesmith]

Nice one. Ironically mine's started sticking now! I only noticed because the outer pad is worn much more than the inner, the brake's not binding at all and frees off perfectly. It's the sliding part that's sticking in my case, the piston moves quite freely and in fact I can see it retracting when the pedal's release. The sliding pins both feel perfectly free when the calliper's dismantled, but for some reason it doesn't work properly when assembled.