Emails are pouring into MPs’ boxes from disabled people and carers, who are truly frightened by the suggestions from government sources and ministers’ speeches that the benefits they rely on are to be cut.

The latest comments to a journalist from someone described as a “government insider” demonstrate starkly what a tin ear some ministers have on this issue. This person accused Labour MPs who are expressing their constituents’ concerns about proposals to cut benefits of “pearl clutching”.

It’s clear that some politicians have learned nothing from the winter fuel payment debacle that is still being raised angrily on the doorstep with Labour canvassers. More importantly, they appear to have learned nothing from the introduction of the work capability assessment for disabled people, associated with nearly 600 suicide deaths in England between 2010 and 2013.

As so many have said, the callousness of this treatment of disabled and sick people is not the Labour way. It prompts the question: why become a Labour MP if you are to vote for a policy that flies in the face of all that Labour has ever stood for?

We’ve heard that there is a moral argument to justify the government’s plans. There is definitely a strong moral argument for providing professional and empathetic support to help people get into work if they are capable of doing so. There is no moral case for propelling even more people into poverty by cutting benefit levels, or denying access to financial support to those who have no alternative.

The lack of understanding and empathy in the government’s policy planning and articulation has been shocking. Report after report has been published by thinktanks and specialist charities, including the Institute for Employment Studies, the Resolution Foundation and the Joseph Rowntree Foundation, to explain the plight of sick and disabled people; how the numbers have risen and the best ways to tackle this issue.

Although people are living longer, they are not necessarily living longer healthy lives. The increase in the retirement age has meant that many simply cannot physically manage to work until their retirement age. The rise in young people claiming benefits for sickness and disability, especially related to mental health conditions, has to be understood in the context of this austerity generation coming on to the books.

Throughout my time as shadow chancellor, I, along with many charities and professional bodies, highlighted the impact the massive cuts in social care were having. They prevented those early interventions to support families and young people by social workers and expert specialists that could identify and tackle emerging problems before they worsened.

We are now reaping the cumulative impact of the austerity measures sown by Tory chancellors. Liz Kendall, the work and pensions secretary, gets all this and appeared to be working to design a system whose underlying principle was supporting sick and disabled people, not penalising them. She recognised that this needs investment in the short term to bring the professional resources together, but that it would pay off in the longer term.

The health secretary, Wes Streeting, obviously gets it because he was putting in place an extra 8,500 mental health workers to address the mental illness challenges we have within our society.

All that meaningful, positive, policy preparation seems to be being ridden over roughshod by the Treasury, whose demand for cuts appears to have risen from the £3bn planned by the Tories to £6bn now. The obsessive and misjudged adherence to out-of-date fiscal rules by the Treasury is knocking this government off course.

Ruling out increased taxes on the wealthiest when groups such as the Patriotic Millionaires are calling for them also appears dogmatic and foolish. And with such an overwhelming majority in the Commons, Keir Starmer and Rachel Reeves have no fear of losing any votes in parliament.

However, many Labour MPs are waking up to the fact that moves such as cutting the winter fuel payment, and now disability benefits, could very easily lose them their seats. Reform UK could exploit the unpopularity of these policies and build a base in their constituencies to springboard into the next election.

There are only a few days left before the publication of the green paper on welfare benefits and just over a week before the spring statement.

There is still time for the Labour cabinet to act like a cabinet, and for its members to stand up to the Treasury to halt the cuts in benefits to the sick and disabled, and to insist on a more flexible interpretation of the fiscal rules and a limited set of tax measures. That would follow Starmer’s guiding principle that the broadest shoulders should bear the heaviest burden.

• John McDonnell is MP for Hayes and Harlington. He was Labour’s shadow chancellor from 2015 to 2020