You might not have heard it but, amid the noise of Brexit, the government is planning a multibillion pound overhaul of disability benefits. The Department for Work and Pensions (DWP) has published a contract notice worth £3.1bn for private companies to bid to win a seven-year contract to conduct multiple benefit assessments. At its heart appears to be a full-scale transformation of disability social security. There are currently two separate assessments for the two key disability benefits – personal independence payment (PIP) and employment and support allowance (ESA). This contract will see a “one-stop” test for both and was issued a few weeks after work and pensions secretary Amber Rudd launched a small-scale trial to test the feasibility of a merger.

For years, MPs and campaigners have stressed that the disability benefits system is in need of widespread reform (70% of ESA and PIP appeals overturn a rejection at tribunal) but it is hard to imagine how combining the tests for two failing systems will achieve anything other than cost-cutting. It is reminiscent of an inventor soldering two corpses together and expecting the body to spring to life.

Fundamentally, PIP and ESA are benefits with two entirely different purposes: while ESA is designed as an income replacement for people who are too sick to work, PIP has no link to employment status and is meant to pay for extra costs of disability, such as higher heating bills or care fees. For a government with a competent record on “welfare”, it would be hard to see how a combined assessment could effectively keep the integrity of each crucial benefit. As it is, this is being proposed by a DWP so “shattered” by repeated failings that last month the thinktank, Demos, recommended that the department be stripped of its duties to even deal with disabled benefit claimants. To ministers, large-scale reform may seem like abstract policy planning but to the disabled people relying on these benefits, it’s as real as whether they’re going to be able to afford regular meals.

Talk to disabled claimants about a merger of the tests and the reaction is one of real fear that has led to the launch of a petition against it. Many are already falling into destitution after being rejected for one of their disability benefits. The move would potentially see disabled and chronically ill people being denied both benefits at the same time, losing much of their income at once.

New disabilities minister Justin Tomlinson. ‘It was only after pressure from charities that the post was replaced’ Photograph: PA

This risk is only increased by the fact the contract suggests disability benefit applications will be moving online through a “DWP-owned single digital platform”, despite the fact official figures show that one in five disabled adults had never used the internet in 2018. Ahead of such large-scale reform, any government should be preparing to put its very best person on the job. In fact, weeks after Sarah Newton resigned as minister for disabled people over Brexit, it was only due to pressure from charities that Theresa May eventually replaced her. The Conservative deputy chair, James Cleverly, had said the post would be left unfilled until Brexit was resolved, before the government U-turned last week and appointed Justin Tomlinson (the sixth person in the job since 2013).

If the revolving door nature of the post has long been emblematic of the cack-handed nature of this decade’s disability benefit reform, having no minister was crassly symbolic of the government’s attitude towards disabled voters. As one disabled reader remarked to me, it is hard to imagine the government saying it could manage without a defence minister until after Brexit.

And that, perhaps, is the real crunch. After years of pulling billions from the “welfare” budget, whipping up “scrounger” rhetoric, and wrongfully withholding disability benefits, there is no trust that new “reform” will do anything other than hurt disabled people more. The disaster of universal credit should surely be a warning in how large-scale mergers can soon end in crisis for those they purport to help.

• Frances Ryan is a Guardian columnist