Fixed dripping, screeching and v.low hot water flow rate
We easily dismantled the shower controls, extracted the cartridge and cleaned the water strainers but this did not improve the situation.
We searched Google for the answer and found that others reported success with the same problems by replacing the central cartridge.
We ordered this part from TheShowerDoctor, it arrived in the next day as promised, we easily fitted it in 10 mins with a screwdriver and now we have a fully restored shower!