The learning disability sector is “under threat as never before”, according to Derek Lewis, chair of Mencap.

Lewis spoke out today as part of the sector’s continuing dispute with the government over who should fund £400m of back-pay for care workers that provide overnight sleep-in support.

Mencap has claimed that, besides the threat posed to charities that employ sleep-in carers, the issue could also affect up to 100,000 families who pay for sleep-in support through personal care budgets. Some, it says, might face bills of up to £50,000.

The row has been simmering for several months after the government changed its guidance on sleep-in care workers. Until recently, most overnight care workers received a flat rate of £35 to £45, according to the Voluntary Organisations Disability Group, which represents charities that provide services to people with disabilities.

But after two employment tribunal decisions, the Department for Business, Energy & Industrial Strategy changed the guidance to say staff should be paid the national minimum wage. Sleep-in staff are now eligible to claim for loss of earnings dating back six years.

Mencap began paying the national living wage in April, but Lewis said it would “cause us severe problems” if it had to foot the bill for six years of back pay. He warned that a number of major care providers could collapse unless the government stepped in.

Ministers, said Lewis, had previously issued incorrect guidance and the government should therefore pay. “For a government that spent £780.3bn in the 2017 fiscal year, £400m doesn’t seem like much to ask,” said Lewis.

He said families and care workers were suffering growing uncertainty and anxiety while the issue remained unresolved. Charities also faced uncertainty, he said. Voluntary organisations account for about 60 per cent of the 200 care organisations affected by the ruling.

“The learning disability sector is under threat as never before,” said Lewis. “For Mencap, it is the worst crisis that the charity has faced in its 70-year history.

“About 178,000 people across the UK have serious learning disabilities and depend on the care that charities like Mencap provide.

“At Mencap, we worry about the effect that this is having on our staff, families and the people we care for. Our care workers do a fantastic job and we want to pay them fairly. Since April we have been complying with new government guidance and paying the national living wage, but trying to fund six years of back pay would cause us severe problems”.

Last month BEIS announced “exceptional measures” to “minimise disruption”. These included temporarily suspending HMRC enforcement action over payment of sleep-in shifts until 2 October and waiving historical financial penalties against employers who underpaid workers for sleep-in shifts before 26 July. But organisations still face the prospect of having to find £400m after 2 October.

A statement from BEIS said: “The government will continue to look at this issue extremely carefully alongside industry representatives to see how it might be possible to minimise any impact on provision of social care, and ensure that action taken to protect workers is fair and proportionate.”