Theresa May’s social care package fails "to tackle the biggest problem” facing elderly people, the man who carried out the coalition’s review into service in England has said.

Sir Andrew Dilnot's castigation of the policy comes as the Prime Minister prepares to publish the Conservative manifesto for the general election, pledging to significantly raise the threshold of personal assets at which people will be eligible for state help with residential care costs from £23,250 to £100,000.

David Cameron had proposed a cap of £72,000, delayed until 2020, but Ms May will now argue that limit – proposed by Sir Andrew, in an independent review in 2011 – is no longer needed.

On the election campaign trail the PM had said politicians could no longer “duck the issue” and that the Government had been “working on a long-term solution” for the needs of an ageing population.

But Sir Andrew said he was “very surprised” by the new thinking from Downing Street. “New thinking that I’d argue shows a less than full understanding of the problems when there is a green paper that is due to come out later this year,” he added.

Speaking on BBC’s Radio 4 Today programme, Mr Dilnot, who is also a former head of the UK Statistics Authority, said: “The disappointment about these proposals that we’re expecting to hear in the Conservative manifesto later is that they fail to tackle what I’d argue is the biggest problem of all in social care, which is at the moment people facing a position of no control.

“There is nothing you can do to protect yourself against care costs, you can’t insure because the private sector won’t insure it and by refusing to implement a cap, the Conservatives are now saying that they are not going to provide social insurance for it so people will be left helpless knowing that what will happen is that if they are unlucky enough to suffer the need for care costs they will be entirely on their own until they are on their last £100,000.

Mr Dilnot said he was “very disappointed” by the proposals in the manifesto – due to be released later on Thursday. “Not personally. I feel very disappointed for all of us – the millions of people who are very, very anxious about this,” he added.

Citing Ms May’s conference speech last October at the Conservative conference, in which she outlined the “good” that government can do and her willingness to intervene in “dysfunctional markets” when they are in need of repair, Mr Dilnot continued: “This was an absolute open goal for that kind of approach and it seems to have been missed.”

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Asked whether people would be better off under the Conservative plans to overhaul social care, Mr Dilnot added the new means test will help some people the “majority” of people getting care in their own home will find themselves “worse off”.

“The changes are not bad in themselves,” he said. “It’s just that they fail to tackle the central problem that scares most people.”

Responding to the proposals, Barbara Keeley, Labour’s shadow social care minister, said: “In their last manifesto they promised a cap on care costs. But they broke their promise, letting older and vulnerable people down.

“It’s the Tories who have pushed social care into crisis; their cuts to councils have meant £4.6bn axed from social care budgets between 2010-2015, leaving 1.2 million people struggling to get by without care.”

Sir Andrew also told the BBC he was unaware of the proposals from the Conservatives until they appeared in the media.

"The analogy is a bit like saying to somebody you can't insure your house against burning down, if it does burn down then you're completely on your own, you have to pay for all of it until you're down to the last £100,000 of all your assets and income," he said.