OH GOD, how awful !
That is such a terrible shame ! It is one of the areas we were thinking of buying too !
Is there some sort of list, some book in the town hall, some sort of assurance that what you buy is all legit ?
If not, why not ?

I realise that these things happen due to unscrupulous people, backhanders, etc !
It happens here to, a friend of ours just had a house fire in Inverness, due to a boiler, fortunately not too serious, but it got much more serious when the tried to get it repaired.
A new boiler could not be fitted, the pipework for the gas was illegal, not due to it being an old property because it is not, it's only 12 years old.
But whoever built it, put all the gas pipes under the foundations and they were too narrow to be legal. Plus they should be accessible which they are not.
You just can't count on anyone not to cut corners !