Flammable material has been found on a group of Norwich apartments, leaving owners with potentially huge bills.

Leaseholders at the Read Mills development on King Street have also been told that their insurance premiums are increasing by 230pc this year to more than £1,400 each, because of cladding issues.

The double blow to the 150 flat owners came after they paid more than £60,000 for a fire safety survey. Without passing the survey, no-one can buy, sell or remortgage.

That survey found that “combustible materials” were present in the external walls and work would be needed. The buildings were rated as B2, the lowest of four ratings. But it is not clear what will need doing, how much it will cost, or who will foot the bill.

The development is managed by Norwich Residential Management (NRM) which said in a letter to residents that there was no immediate risk to them but a plan was being drawn up by a fire engineer to carry out “remedial works”.

NRM told residents that a sample of cladding was being sent to a lab for testing.

Tony Millings, of Albion Mill, said: “It is a concern knowing that it has failed this safety test, but you think, how is a flat which has been here for years now failing a fire test?

The 52-year old procurement manager added: “I don’t lie awake at night, thinking the place will burn down but my big concern is I now could have a worthless property with big repair bills."

NRM said there were three options to pay for the work. They could contact PJ Livesey, which completed the development in 2009, ask the freeholder or use a government loan scheme, but that would leave leaseholders in debt.

One of the six buildings, Cannon Wharf, is over 18m high and eligible for a government fund to remove cladding.

Buildings below 18m can apply for a government finance scheme, which would mean the leaseholders effectively borrow for the cost of repairs, repayments capped at £50 a month.

However, the schemes do not cover the costs of any other fire safety issue.

The report has not been given to the residents, but NRM said they would be provided with the “relevant information” from it.

A PJ Livesy spokesperson said: "All apartment buildings are now being inspected in the wake of the Grenfell tragedy and the majority are found to be B2 rated which require further investigation.

“We completed the conversion of Read Mills in 2010 and do not own the freehold and so would not expect to see a copy of the report.”