Iain Duncan Smith, the work and pensions secretary, is poised to announce a radical reform of sickness benefits that the government hopes will force up to 1m more disabled people into work. Changes to employment and support allowance (ESA) and the assessment of people claiming sickness benefits will be part of a package of announcements expected to be made public on Monday, which aims to shrink the “disability employment gap” by taking many people off benefits and expecting them to move into work. The reforms will anger disability campaigners, who claim that they are being targeted as part of a £12 billion cut in the welfare bill.

The changes come days after the Department for Work and Pensions admitted it had used made-up stories from fictional claimants to demonstrate the positive impact of benefit sanctions. On Thursday, the DWP is expected to release data for the first time showing how many disability benefit claimants have died after having their benefits cut or stopped.

In a speech on Monday, Duncan Smith is expected to claim that 2m more people are in work and that the number of workless households is at a record low following previous government reforms. “There is one area on which I believe we haven’t focused on enough – how work is good for your health. Work can help keep people healthy as well as help promote recovery if someone falls ill. So, it is right that we look at how the system supports people who are sick and helps them into work,” he is expected to say.

“But we must not stop there. We need to be relentless in our efforts to get more people into work and off welfare,” he will say. “The number of disabled people working has risen by 350,000 over the past two years, the highest on record. Yet, even though we have got more disabled people into work, that is only the beginning.” According to a briefing, Duncan Smith will also announce new changes to the Fit For Work service and changes to access to mental health advice for claimants.

Last week, the DWP admitted using made-up stories from fictional claimants to demonstrate the positive impact of benefit sanctions. A DWP leaflet featured one welfare claimant, “Sarah”, who said she was “really pleased” a cut to her benefits had encouraged her to improve her CV. But after a freedom of information request by the website Welfare Weekly, the DWP said they were not real claimants. The stories were for “illustrative purposes only”, it added.

Under the sanctions system introduced by Duncan Smith, people can lose benefits for up to three years if they fail to meet the government’s requirements for jobseekers.

Statistics showing how many people die while claiming out-of-work disability benefits will be published on Thursday. The information commissioner overruled attempts to withhold the statistics, originally requested by a campaigner using freedom of information laws. The DWP said it had always intended to publish them.

In April, the commissioner asked the DWP to publish the number of claimants of incapacity benefit and employment and support allowance who had died between November 2011 and May 2014. The initial freedom of information request was sparked by concerns that disabled people were being declared fit for work, having their benefits stopped, and then dying. The prime minister, David Cameron, promised in June to publish the figures.

The so-called disability gap is the difference between the employment rate for people with disabilities and those without. According to an analysis of figures from the Office for National Statistics by the disability charity Scope, 48% of disabled people are in employment, compared with 73% of the general population. However, disability rights activists have called for the government to do more to normalise perceptions of disabled people at work, rather than treating the situation as “a problem that needs to be explained away to employers”.

A DWP spokesman declined to discuss the figures in Duncan Smith’s speech or release further details. A spokesman said: “This isn’t a policy announcement; it’s the start of a conversation.”