Thanks.

Before you posted I had taken the pads out, given them a clean and a rub on some wet and dry paper, and then cleaned the caliper with brake cleaner. The pistons looked like new, although I don't have a brake pad spreader and I couldn't move the pistons by hand. Reassembling everything, there was definitely more feel in the brakes, although still not on the same scale as most other bikes I've ridden. After a 3 minute ride round the block with a bit of braking, the disc was almost too hot to touch. I don't know if this is normal, or whether it's indicative of the pistons not retracting properly and keeping light pressure on the disc. Maybe this is what glazes the pads?

Should I be able to move the pistons by hand without a screwdriver or pliers? How do I know if they're a bit sticky?