Yes of course he should have had the correct forms, insurance etc.
But it was a nice house, they lived there happily. "Spacious, no mould".
If there was anything wrong when they first moved in they would've told the landlord : there's a problem with the electricity or the gas..... there are no smoke alarms ......
They didn't do any of these things which implies that the property did have smoke alarms or seemed safe?
and they lived there quite happily for eight months and and continued to live there whilst suing him, it says.
Do not do dangerous they had to threaten to leave, then? 
then they later found out that he didn't have a certain form?
but if there been any problems how come they lived there happily for eight months?
something just doesn't add up here.