On 10 Feb, 18:23, " wrote:
Your points 1,2 and 3 are LEGAL REQUIREMENTS. The building regs
specify solid fuel appliances MUST be twin wall, MUST have permanently
open vents, MUST be 6" or more diameter.

What was specified in the contract? I'd be reaching for a lawyer in
your position - and shopping them to building control. And as they've
proposed a fraud - possibly the police.

If they've fitted a single wall liner intended for gas appliances, it
may well fail in a few years time - there's damn good reasons for most
of the building regs requirements.

Actually, points 1 and 3 aren't legal requirements. The installed flue
is a cast in situ refractory concrete liner, the diameter being 7".

They not only proposed a fraud, but I have the fraudulent certificate,
and the fraudulent safety information notice.