After looking at my wheels I could see loads of brake dust on the rear left and only normal amount of brake dust on the other side. The alloy wheel itself and the caliper were very hot. A couple of weeks before I changed the pads and noticed that the piston was very stiff to rewind almost impossible.. any ideas what to try or will the caliper need replacing?

I had the same , it bothered me for a while until I discovered that the h/brake cable on the nearside had been adjusted right up. The offside one was normal , how they got like that I've no idea,. took off all the adjustment , also freed off the piston and cleaned it , replacing the dust cover. Fitted it all back together and worked the pedal then adjusted the h/brake and it was like a new car ( h/brake wise )

Now I'm confused, it's only starting happening since I changed the rear pads do you think this could still be to do with the handbrake? How easy is it to replace the dust cover and clean off the piston?

An easy couple of hours taking your time will see the job done, I've a post somewhere detailing a rear caliper piston out, clean up and reassembly.

Sounds like the pads or caliper are sticking.

I had a similar problem on the NSR and taking the pads out, cleaning and lubeing seems to have sorted it. I didn't have an issue with the caliper: that moved freely.

The pads needed fileing down to metal where the connect with the sliders and a suitable amount of copper grease applying.