Hi,

Thanks for replying

1) Was there no fire connected to the flue before?

No - it was an electric fire. The flue was boarded up behind the
electric fire.

2) If there was (and it seems highly likely, considering it's a flue) why
did the plaster not crack then?

Maybe before the electric fire, the previous fire wasn't a "living
flame" effect fire, and didn't send as much heat up the flue. I

3) How do you know the plaster is cracking after 30 mins?

Because the plaster is cracking off the wall.

What is different between the two flues from 1975 and 1986?

Building regulations released on 1975 say it's okay to plaster directly
onto the flue. They were revised in 1986 when "living flame" fire
became popular - people where complaining about cracked plaster.

Anyway. according to trading standards, borough building department,
and corgi technical help, the seller/fitter cannot be held responsible
for mis selling the goods as he wasn't possible to determine if the
plaster was stuck to the flue or not when surveying.

Balls.