Someone's been told by 3 developers that "the building regs won't let
them put them in new build flats"

I have not been able to find any reference to a gas installation ban for
tall buildings anywhere in the building regulations or the Gas Safety
(Installation and Use) Regulations.

What I have found out, is that after the Ronan Point collapse, tall
buildings (over 5 stories) had two options. They either had to be able to
cope with explosions of 5psi, or alternatively, cope with explosions of
2.5psi and have the gas supply removed.

I can find nothing to suggest (and plenty to suggest otherwise) that new
build flats can't have a gas supply, provided that any building over 5
storeys meets the 5psi explosion resistance requirement. I believe the
option to survive only 2.5psi and have no gas might only be applicable to
existing buildings (in 1968).

Christian.