Razi said:The engineer is willing to fit 5 thermostatic valves on the radiators for extra £70.
Thermostatic valves on all rads except the one in the room where the room stat is, is mandatory to Part L energy efficiency regs and basic CHeSS.
Sounds like the installer doesn't know the regs.
At that price and if it includes VAT then bite his hand off IF you are sure he is all he says he is