After reading your post again, with a bit more attention this time, I
notice you say one wall will form the boundary of your property. It
would then fall under party wall legislation and may be a problem to
build without special planning permission.

I was under the impression that the Party Wall Act was a toothless tiger
and, in any case, didn't affect what you could build, just the way that you
inform your neighbours.

I take it you do have planning permission already for your proposed
original site ? If not, stop even thinking about building anything
until you do.

I've still seen nothing to suggest that I need planning permission at all.
The proposed conservatory is well within the requirements of my available
permitted development rights and would be so even if made of brick as a
proper habitable room, as I understand it.

My advice to you is, "you should now go to an actual company that does
them for a living, and ask how they go about building one of these things".
Put your mind at ease.

Because I can build one for 4,000 quid myself or pay some scrote with only a
mobile phone number 15,000 to do it for me. This is uk.d-i-y you know!

The only things left for me to find out a

a) What's the definitive answer to the building regulations question? (i.e.
does it need approval, what are the rules applicable).

b) How should I construct the floor/foundations and attach the conservatory
to them?

I've just looked again and I have about 30cm available for a concrete floor,
Jablite and DPM, which I hope is enough.

My guess at the moment is that you construct a concrete floor, with DPM
right to the edge, about 20cm above ground level and just attach the wood
frame to the concrete. Any problems with this? Would a suspended wooden
floor be better?

Christian.