Social care is “under threat” in parts of the country, No.10 has admitted – paving the way for council tax rises next year to rescue services.

The growing controversy provoked the "lengthiest discussion" among ministers at Tuesday's Cabinet meeting, Theresa May's spokeswoman said.

It is the first time ministers have acknowledged the “threat” to social care systems, having previously preferred the phrase “under pressure”.

And it came as Simon Stevens, the chief executive of NHS England, said care services – rather than the NHS - should be at the "front of the queue" for any Government cash injection.

He told a House of Lords inquiry: “It is quite obvious that the knock-on consequences of a deteriorating social care offer - not only for vulnerable people, but also into hospitals - is now unarguable.

"I think there is a very strong case for some immediate support now."

Town hall chiefs are known to have discussed proposals with ministers to fill a black hole in funding for adult social care expected to reach £2.6bn by 2020.

They are strongly rumoured to include increasing the current two per cent "social care precept", an extra levy on council tax introduced by George Osborne last year.

One possible option is to scrap the limit on the precept altogether – prompting speculation that the typical bill could rise by up to £100 a year, in an announcement on Thursday.

Ms May’s spokeswoman insisted it was possible for councils to “provide high quality social care within existing budgets if reform was followed through”.

But she added: “The ability to provide social care for local communities is under threat and Thursday's announcement on the local government finance settlement will address this issue while making clear the need for reform.

"The PM emphasised the importance of finding a long-term, sustainable way of addressing the issue."

Asked whether councils in under-pressure areas would be allowed to increase the two per cent precept, the spokeswoman said: "I suggest you wait for Thursday's announcement."

There have been widespread warnings of a social care crisis, with the closure of 250 residential care homes since March and the loss of 5,000 beds over the past 18 months.

The number of days hospital patients wait on wards for suitable home care packages has soared by 224 per cent since 2010.

And the chief executive of Care England, which represents care home providers, warned that rising demand, combined with spending cuts, have created a "house of cards".

Conservative ministers and MPs, fearful of a public backlash, have been lobbying Downing Street to find a long-term solution.

Only yesterday, Downing Street played down talk of a crisis, arguing just 20 local authorities are behind half of all delayed discharges from hospitals because of a lack of available care packages.

Last month, the Prime Minister told Jeremy Corbyn that '“social care funding is going up”, while Labour had pledged to freeze cash for local councils at the last election.

The Treasury has insisted councils will gain an extra £3.5bn of social care funding by 2020, money diverted from the NHS under the ‘Better Care Fund’.