Boris Johnson’s flagship plan to fix social care will benefit a fraction of the people who need help, the Observer can disclose, as charities and campaigners urge ministers to act now or see thousands being left without any care at all.

After it comes into effect in 2023, the new policy will directly help about 150,000 more people at any one time, according to government documents. But already about 850,000 older people who receive care have at least some of the cost paid by local authorities.

Age UK estimates that a further 1.5 million older people need care but are ineligible for support – up from about a million in 2014. Some pay for it themselves, some get help from their families and some go without any care at all.

But while the prime minister’s GBP36bn national insurance tax rise focused on how care will be paid for after 2023, he made no provision to ensure that the sector survives the crisis engulfing it now.

A new Opinium poll for the Observer, taken after Tuesday’s announcement of a 1.25 percentage point NI rise, suggests that the healthcare levy may be harming the Conservatives in the polls and benefiting Labour, which has yet to lay out its social care proposals. Today’s poll puts the two parties neck and neck. The Tories, who held a five-point lead a week ago, are down two points at 38%, with Labour up three at 38%. The Lib Dems are on 8% with the Greens on 6%. This is the first time the Tories have not been in the lead since 15 January.

Opinium’s leader approval ratings also show Johnson dropping to his lowest-ever score: 17. 49% now disapprove of the job he is doing (up four points) while just 32% approve.

Disquiet has grown among Tory MPs and supporters over recent days, as they question when and by how much the social care system will benefit from the extra money.

There is also mounting concern that council taxes will have to rise from next spring to help local authorities pay care costs, and to avoid another round of deep, punishing cuts in other services. The care plan announced by the government last Tuesday explicitly pointed towards council tax having to take extra strain over future years.

Tory MPs in former Labour seats fear that working-age voters who switched to their party at the 2019 election will feel betrayed at having to pay more tax when they were promised that a vote for the Conservatives would see them benefiting from Johnson’s “levelling up” agenda, and avoid the higher taxes a Labour government might have charged.

Kate Ogden, a research economist at the Institute for Fiscal Studies, told the Observer: “The government’s announcement of an extra GBP5.4bn for social care over the next three years should help councils across England to reverse some of the significant cuts made to adult social care during the early-to-mid 2010s, which left spending per person 7.5% lower in real terms in 2019-20 than a decade earlier.

“However, this plan is far from offering a sustainable funding solution for the local government sector as a whole. Buried in the detail is the suggestion that councils will still be expected to meet demand and cost pressures through council tax rises and efficiency savings.

“Unless more generous funding for councils is announced at the upcoming spending review, we can still expect significant council tax rises in the coming years, if rising needs and the myriad of pressures facing other council services are to be met.”

A deepening shortage of care workers – many are leaving the sector to work in better-paid jobs in supermarkets or delivery firms – means that many care providers are having to turn people away.

Vic Rayner, chief executive of the National Care Forum, said: “There is an immediate pressure on social care that the government doesn’t seem to recognise, even though we can see the problems emerging before our eyes.”

Sally Warren, director of policy for the King’s Fund, said: “The [extra] 150,000 people who will directly benefit from the new cap and extended means test is a significant increase on the 850,000 people who currently get some financial help with their long-term care.

“But the government’s plan this week has done nothing to tackle the high levels of unmet need in the country. There are estimated to be as many as 1.5 million people with unmet need and the government’s plans need to ensure that the system can support more people to get access to the care and support they need to live good-quality lives.”

Those working in social care hope that in his 27 October spending review Rishi Sunak will announce extra funding for the sector. The government paper, entitled Build Back Better – Our plan for health and social care, says that in addition to the 150,000 who directly benefit, “everybody will benefit from the certainty and security that if they or their loved ones need personal care, they will no longer face unpredictable and unlimited costs”.

Case study: ‘People a bit later in life could have shouldered more of the burden’

Jonny*, 25, is one of thousands of graduates who face paying 42.5% of their earnings in tax and student loan repayments after the government announced changes to the rates of national insurance to fund social care.

He recently landed his first job after completing an MA in PR at Cardiff University and is paying back his GBP35,000 student loans from his earnings, as well as income tax and national insurance, along with half of the rent on a studio flat in Kilburn, north-west London. The 1.25 percentage point increase will increase the rate at which he pays NI to 13.25% from next April.

“I’ve worked it out and it will add between GBP200 and GBP300 a year to my costs,” he says. “Our rent is GBP1,075 a month between the two of us, and there’s all the bills on top of that: electricity, gas, council tax, the internet – which I need for my job. At the moment, I’m not left with much after that to get by.”

He stresses that he is not badly off compared with some of his peers, and hopes that the time he spent at university will see him progress and earn more, although the student loans could still take 10-20 years to pay off. And he is a fan of the NHS. He saw his grandparents get good care from it in their later years, and praises the community nurses who visited them on their days off.

“It’s tricky – I get that it’s not an easy decision to make, but there could have been a fairer way,” he says. “The younger generation faces lots of barriers. I know people who have just graduated who are struggling to find a place to start their career. Maybe people a bit later in life could have shouldered a bit more of the burden.”

* Surname withheld