Andy

Many thanks for your time on this.
From the figures you give I am a little more reassured.

However I would appreciate it if you could look up the following:

Floors

All floors are uninsulated ie plain concrete (due to pipe leaks we even had
to lift all the original vinyl tiles!)
The basic house dimensions a
8m square in plan with front elevation facing approx east
There is also a single storey kitchen extension to the north which has three
exposed walls - north wall 5.5m long and east/west walls 4m long.
Finally, our room is over a garage, constructed in an extension before we
bought the property. Do you know the likely floor construction for this
room bearing in mind building regs requirements and hence the likely U Value
for heat flow down from this room?
The garage ceiling has been plastered with a plaster board "return" down the
wall which adjoins the original house about 2 ft deep. Presumably the joist
cavities will have been insulated to meet regs (it certainly doesn't feel
like it as the cold weather arrives!)

Thanks again

Phil