Becky89 is right, thermostat dials are not accurate ways of measuring the temperature. Their function is really to just keep temperatures stable to prevent over/under heating. Which is why you need an accurate, digital thermometer to work alongside the thermostat. This will give you a much more accurate idea of your temperatures, then you adjust the thermostat accordingly.
I'm sure there are a few exotic vets around London, in the general herp section, on the stickies I think there's a couple of threads with a list of vets on