In general as said before the standard rate has been 10 to 15 pounds an hour for the last couple of years.
However lately there are signs that instructor pay is starting to pick up; two schools (one advertised in Flight International) another one on the BALPA webiste were advertising rates of 24 to 28 pounds per hour flown. Plus another advert on pprune itself was advertising a salaried position, with flight pay extra to the salary. Lets hope these are not one off "generous" offers but a sign of improving conditions. Possibly the increase in SSTR schemes in the airline industry may be reducing the supply of instructors.