Hi there , i have a 2007 07 plate mondeo st tdci , the rear brake callipers were old and sticking a little so i bought 2 new callipers and fitted them , one side is fine but on side is sticking really bad , sliders and pads etc are all free , any ideas thanks

Double check the sliders, first of all. They can seem to be sliding freely, but if you take the slider out and spin it in a drill on a low speed, even a slight bend will become evident. If they are slightly bent, they just won't work right.

I have a theory that garages who change brake pads cannot be bothered to take the caliper off properly to wind the piston back in, so they just take one pin out, swivel the caliper up, and push the piston back in against the other guide pin, bending it.

Other than that you could try undoing the bleed valve on the caliper to see if brake fluid sprays out (put a bit of hose on the valve to direct it into a container, or something). There should be no pressure in there at all, and very little if any brake fluid will come out. If there's a significant amount then you could have a problem with the flexi hose (the insides can go bad, and prevent the fluid returning).

My money's on a slightly bent guide pin at the moment, though. Seen it several times before.

How's the handbrake cable?