Building insurance

My mate lives in a flat, in a Victorian terraced house, which has seen better days - but the three flat owners bought the freehold off the previous negligent owners and are slowly doing it up.

Earlier this year they had a man round to see if they could claim on the building insurance for problems with the roof/guttering. He said no - so they are now getting a decent roofer in to fix that in the next month and split the cost across the three flats.

Trouble is, the man who came round said the property hadn't been maintained properly in line with the building insurance, told the insurance company this, and a letter arrives yesterday saying the insurance company have cancelled the insurance backdated to Feb - invalidating of course all three sub-mortgages at least: at worst making it now more difficult to get building insurance elsewhere as they've been now been refused insurance once.

Any advice on next steps? At the moment they are putting together a schedule of work, contacting the broker this morning, and in addition thinking of getting their own independent survey of the building. Anything that involves cost takes time as it has to be agreed by all three flat owners who are at least engaged now in the upkeep of the premises to varying extent. Trouble is what they need asap is... building insurance.

Any advice very gratefully received. Clearly they are not going to be the first people this has happened to..... many thanks!