The Tory rebellion on social care poised to erupt in the Commons on Monday night is set to spread to the Lords, where former ministers will attempt to force a Government climbdown.

       Lord Lansley, a former Conservative health secretary, and Baroness Altmann, an ex-pensions minister, told The Telegraph they would seek to amend the legislation when it arrived in the upper chamber next month.

       It comes with Boris Johnson set to face a Commons revolt after ministers put forward changes to the new social care system which MPs said amounted to "changing the goalposts halfway through the match".

       The changes, set out in a government document, revealed means-tested support would not count towards the ￡86,000 lifetime cap on care costs.

       Dan Poulter, a former health minister, and ex-chief whip Mark Harper are among Tories set to rebel. Mr Harper wrote on Twitter: "It potentially disadvantages the less well off and those of working age with life-long conditions. I will be voting against it."

       Tens of Tory MPs are said to be minded to rebel or abstain in the vote, expected to take place at around 10pm.

       ‘They're left trying to shift the narrative rather than set it’

       Meanwhile, a blame game erupted as government sources claimed the Department of Health and Social Care had failed to sell the benefits of the policy to MPs. An insider said the department had been "behind the curve" in its briefing operation, adding: "Now they're left trying to shift the narrative rather than set it."

       Many Tory MPs fear the new system will advantage wealthier pensioners at the expense of those with more modest assets.

       The economist Sir Andrew Dilnot, who initially drew up reforms designed to prevent people losing their homes to pay for care, said the latest changes to the proposed care cost cap will hit anyone with assets of less than ￡186,000 – about 60 per cent of older people requiring care.

       One Tory said there was "a lot of discontent", while another predicted: "This has got legs. It is picking up a head of steam. It will run – the Lords will do lots of things." Some planned to abstain rather than rebel in the expectation that the Lords would send the legislation back to the Commons for reconsideration.

       The Government has so far refused to publish an impact assessment of the plans. On Monday, Downing Street said that would happen at a later date.

       Earlier in the day, Mr Johnson said his plans for reform of social care funding were "incredibly generous" and "much better than the existing system", which does not offer protection against soaring costs.

       Paul Scully, the business minister, said the reforms would lead to "fewer people selling their houses" to pay for care. The 2019 Tory manifesto said social care reforms must "guarantee that no-one needing care has to sell their home to pay for it".

       Jeremy Hunt, a former health secretary, said that although the changes made the system "slightly more stingy" they were still a "step in the right direction", signalling that he would back the move.

       ‘That is not levelling up – it is daylight robbery’

       Lord Lansley, the Tory health secretary who first commissioned the Dilnot study on a care cost cap, highlighted that the plan he had initially pursued would have meant "nobody would be at risk of losing more than about 45 per cent of their total assets".

       He said: "That is something that I really rather regret that the Government has moved away from. If there is a mechanism by which we can require the Commons to think again, we will do so."

       Pointing out that the Government had introduced the Bill before it published a long-promised white paper on social care reform, Baroness Altmann said: "People are being rushed into it. It's half baked and not very well thought through."

       She warned that "we can assess and always try to address it in the Lords", adding: "We need a policy that will improve social care and make the system work more fairly across the country. At the moment, this does not seem to me to fit that bill."

       Jonathan Ashworth, Labour's shadow health secretary, told Sky News: "If you live in a ￡1 million house, perhaps in the Home Counties, 90 per cent of your assets will be protected if you need social care.

       "But if you live in an ￡80,000 terrace house in Hartlepool, Barrow, Mansfield or Wigan, for example, you lose nearly everything. That is not fair, that is not levelling up – it is daylight robbery."