Residents who have had no hot water or heating for more than six months say they were told "out of nowhere" that they could lose their homes if they did not pay a lump sum in service charges within a day, along with an additional "debt collection fee" of up to £1,000.

About 19 leaseholders at Admiral Court in Croydon, south London, have been without a gas supply since 4 March because of "potentially dangerous leaks".

The BBC recently reported that residents had been caught up in layers of bureaucracy over who is responsible for paying for the remedial works.

Following this reporting, some residents in one of the private leasehold blocks received an email from Grangeford Asset Management - which represents the freeholder - demanding payment of the full year's service charge in one go, despite residents having monthly payment agreements.

The company has been approached by the BBC but has not responded.

Grangeford gave leaseholders less than a day to pay the full amount, with the warning that otherwise "the landlord will begin forfeiture proceedings to repossess your property".

The company has told residents that the basis for demanding the lump sum is the "non-payment of service charge as per the terms and conditions of [the] lease".

Residents say additional costs have also been added as "debt collection fees".

George Ainsworth, 31, and his wife, who is recovering from major surgery, have been washing out of a bathtub using a bucket filled with hot water from kettles for the past six months.

He said he was taking his wife to hospital for her operation when he saw an email in his junk inbox requesting that £3,918 be paid by the end of the day, with a threat that he could lose their one-bedroom flat if he did not.

"They gave us six hours to pay it," he said. "We've just been paying our service charges monthly, as we agreed with the managing agents, and out of nowhere the freeholder's just taken over on recovering service charge and demanded it all in one go with a £1,000 fee on top."

Correspondence seen by the BBC from Grangeford says the difference, which totals £1,000 in multiple cases, "relates to the breach of lease costs... following the account falling into arrears, together with the debt collection fee".

George believes that sum is "made up, as far as I'm concerned".

Russell Conway is a senior partner at Oliver Fisher Solicitors, which specialises in repossession law.

He told the BBC: "Repossession of a leasehold property is exceptionally complex and could easily take up to a year if contested.

"Threats of repossession in a few days is fanciful in the extreme.

"They would at least have to send a letter of action in the first instance. Managing agents and freeholders will do everything they can to recover service charges, but these can be contested.

"In order to forfeit a lease for service charge arrears, the freeholder first has to prove the charges are reasonable and due by going to the first-tier tribunal."

He added: "A demand for £1,000 for collection charges seems awfully high, frankly, because a lot of debt collection agencies work on much lower charges.

"Anyone faced with that sort of charge should immediately challenge it. You can do it online at the first-tier tribunal, and you can challenge that aspect of the service charge."

Conway said there could be other disputable aspects of a service charge, for instance when residents are not receiving basic amenities.

Other residents have told the BBC they feel what has happened amounts to "bullying tactics". They also dispute the charges and say they are being pushed further into debt, but some have paid the money due to fear.

The original developer of the 2019 flat block, UK Land Assets, has gone into liquidation. The freeholder is now pursuing legal action against a number of companies it says are "associated" with the original developer, seeking to recover the cost of the remedial work.

George believes the additional charges, sent a week after the BBC's previous coverage, could be intended to help pay for legal costs.

"Kind of speculating... but the legal avenues they're pursuing are probably quite costly, so they're trying to recover funds as quickly as they can," he said.

"They're trying it on. We think they know there are no repercussions if it doesn't work out for them."

In the meantime, the couple continue to wash out of their bucket.

George said: "I have to think first and foremost about my wife's recovery. And obviously this is a serious situation, so trying to balance the two can be challenging, but nonetheless I have to do it.

"Nobody really understands how this has been able to happen. The flats were sold with gas pipes which didn't function, which violated several regulations."

He added the service charge had already increased almost threefold over the past few years, from around £1,200 in the first year to £3,500.

"It was all rosy when we bought the place," he said. "It was our first property together.

"We didn't have debt collectors on our back, we had hot water, we had the plan that after five years we'd sell and move up to the next step of the property ladder.

"Looks like that plan is going to be delayed."

One block of Admiral Court, a three-building development, is managed by a housing association, whose residents have not received the same emails as George. This is also the case for some of the people living in the two blocks that are privately owned by leaseholders.

Warwick Estates, which manages the blocks and usually collects the service charge, said it was "not part of the decision-making process in question here".

"We would therefore refer you to the freeholder for further clarity," it added.

The BBC understands Grangeford, which represents the freeholder, is now responsible for collecting service charges. It has not responded to multiple requests for comment.