+1 sounds like it's due for a CLA (clean lube adjust)
Over here most people use Eric
Home who does excellent work for very reasonable prices, but there is likely an Eric type somewhere in UK who would be more convenient for you (isn't there a UK Pentax forum separate from this one? It may be a good place to check for more local service techs
Edit - I will point out that in the longer term the proper CLA is cheaper than just replacing as any old body you buy will likely suffer the same fate sooner rather than later, whereas a properly CLA'd camera will not only function better for longer the metering will also be more accurate as adjusting the meter is part of a good CLA