Just had a visit from a very friendly plumber, about replacing an electric
hob with a gas hob.

In passing, he said that he had just had to condemn an installation where a
Polish person had connected the cold mains to the gas part of the boiler,
and the gas to the cold mains feed.
He had told them they would have to call in the gas and water boards and it
would const them £7-8K to sort it all out.

My mind is still mildly boggling over the concept.
[And the £7-8K; I suppose it depends on how long they had it all turned on
before they realised the boiler wasn't lighting and they seemed to have a
lot of air in the water system.]

I am also wondering which is going to cause more problems - mains pressure
water in the gas main or mains pressure gas in the water main.

Not far from November the 5th; exploding water anyone?

"We keep putting water on the fire but it keeps getting worse and now our
hose is on fire".
Alternatively
"The gas cooker keeps putting itself out".

Boggle, boggle, boggle. :-)

Dave R