Good point about square metrage. We seem to be constantly short-changed in this country. And yes, of course developers would take advantage, the bastards.
As for estate agents lying about room sizes, I do wonder how stupid they think people must be. Anyone can see right off whether a room is a single, double or box. They should not be allowed to get away with that.
Perhaps there should be a national standard set for the smallest size one can get away with calling a single/ double, etc. I'm sure the cretins would try to get around that somehow, though.