I am currently having my loft converted, which includes the installation of a shower room in the loft space. My hot water pressure is already low and I am told that it will be even lower given that the tank in the loft will be moved and will be slightly lower than before. The solution, I am told, is to dispense with the tank in my loft and have a new pressurised hot water tank in place of my existing hot water tank. The system then becomes non-vented and relies on the mains cold water pressure, which seems fine. I don't pretent to understand it all but it seems plausible, but comes at a cost - £1500! Any advice on this proposal please?

According to my handy -dandy calculator your plumber wants to charge you the equivalent of $2955.00 to convert your gravity system to a pressurized one. Considering the cost of a electric 40 gallon heater, $400 or 203 pds, and 2 hours installation time plus parts, $175 or 88 pds, the plumbers in your area must all drive Rolls Royces Trucks to a service call and live in large mansions.
Unless there is a lot of work and hassle to changing over your system I would say your plumber's grossly overcharging you. Get at least three estmates before you let the job out. Good luck, Tom