The debate scheduled for 11.15am in Westminster on Thursday represents a significant parliamentary milestone – the first debate secured by disabled people for disabled people.

The motion, set down by the War On Welfare (WOW) campaign group, calls for an assessment of the cumulative impact of the government's welfare reforms on sick and disabled people, and demands an immediate end to the work capability assessment (WCA), the test that determines fitness for work.

Comedian Francesca Martinez has spent a year campaigning to get the 100,000 signatures required to trigger a parliamentary debate on the issue, motivated by concern that the true impact on disabled people of the government's welfare reform programme has never been measured.

Although the fact that the debate has been called represents a considerable triumph, Martinez is concerned the government may try to sweep the event under the carpet. "If the government does try to brush it aside, it will leave you thinking, 'well, what democracy is there?'," she says.

Mike Pennington, the minister of state for disabled people, will speak in the debate but MPs are not obliged to attend or turn up to vote. The petition has been supported by 250 MPs, who include only three Liberal Democrats and no Conservatives.

Martinez, who has a well-established career as a standup comedian, and has cerebral palsy, agreed to get involved with launching the WOW petition because of her anger about the direction of welfare reform.

"It seems we're living in a country at the moment where if you do get sick or if you do become disabled, not only have you got to deal with those challenges but you have to deal with the fact that the vital safety net that society provided for many decades is being eroded away," she says. "Disabled people around the country are dying from these policies." She cites the figure of 10,600 people who died within weeks of being found fit for work by a WCA test. "Many more are falling into destitution and being subjected to humiliation and being targeted in a really awful way."

She contests the argument that welfare reform is driven by a need to cut costs, and points out that since so many people are going to court to appeal against decisions to remove benefits, the savings are negligible. "We have to challenge the government rhetoric on the money-saving argument," she says.

Martinez was granted lifetime eligibility for disability living allowance (DLA) in recognition of the fact that her disability means she needs extra support to live independently. Under the reforms, her eligibility will be repeatedly reassessed, although improvement in her condition is a medical impossibility.

"Reassessing people like me every few years is going to cost millions and it is actually entirely wasted money," she says. She points to the government's willingness to declare money no object in helping victims of the recent floods as further evidence of the weakness of the argument that welfare needs to be reformed on cost grounds. "We need to correct the distortion that there's not enough money in this country. There's more than enough money – there's just not the will to spend it."

Announcing its reform of DLA in 2010, the government said it wanted to cut the cost of the benefit by 20% – a decision that Martinez says will eventually prove more expensive because people will find it harder to get the support they need to work. Her early success as a comedian rested on the fact that DLA helped to pay for a car, allowing her a degree of independence she could never otherwise have had.

"Already, with the benefits, a third of disabled people live in poverty. Now that figure is just going to rise," she says. "Half of disabled people are unemployed. For a lot of people, these cuts mean that they can't leave their house. They will be making decisions like: do I eat, or do I pay for a taxi to get me out of the house? Also many disabled people need extra support to be able to work. So, ironically, by taking away this support network, disabled people are going to be less able to go and contribute and live full lives. On every level it doesn't make sense. You're going to make disabled people more vulnerable and less independent."

The debate is timely, coming a week after the announcement by the private company, Atos, contracted to carry out fitness for work assessments, that it was seeking an early exit from the contract, after criticism about the accuracy of its testing process and reports that staff had been sent death threats.

The company's retreat provides little cause for celebration, Martinez says. "Atos is not the key problem; it is just going to be replaced by another company willing to carry out the government's work." She would prefer people to be assessed by their GPs for eligibility to sickness benefits. "A private company is far more likely to adhere to targets than a doctor will. You want private companies out of this. You need profit out of this."

She is angry at the way that support for disability benefits has been reduced by a campaign of media misinformation. She dislikes the way the very word "benefit" suggests something positive and extra, rather than simply a levelling of an unequal playing field. "I hate the word benefit because it suggests a bonus," she says. "I get benefits because I can't walk out of my house on my own. I can't make myself a sandwich. If you say to someone: 'would you rather get £90 a week, or would you rather walk?' No one is going to opt for the £90 a week.

"The rightwing press has had a huge impact on demonising claimants and demonising disability and disabled people as burdens on the state – useless parasites; we have seen a sustained attack over the last few years. Look at the increase in the use of words like 'scrounger' in relation to disability in news stories – there has been a three-fold increase. The media is rigorously pushing the government agenda on this. It has a profound effect on public perceptions of disabled people."

She points to the proliferation of stories about fraudulent claimants. "Fraud is a non-issue, tiny, under 1% in these benefits. We never hear the truth. The truth is most disabled people really want to work but can't, and all they ever think about is: 'I wish I could work; I wish I could provide for my family; I wish I could feel like a fulfilled active citizen'. It's not a dream of disabled people to sit at home doing nothing. I think that's something we've really got to shift in terms of perception."

Martinez hopes the parliamentary debate will be a chance for Labour to clarify its position on welfare reform. Aware that the WCA was launched by Labour, she knows the party's support for her campaign is far from guaranteed.

"Labour clearly aren't going to play the role of knight in shining armour. They are not going to change anything unless there is huge reason to do so. I don't know where [Ed] Miliband stands on any of this – but slowly we are getting it on the agenda. I'd like the debate to make the top guys in Labour take this on seriously, for Miliband to say: 'if we get to power, we will scrap the WCA'," she says.

Curriculum vitae

Age 35.

Lives west London.

Family Lives with partner.

Education Parliament Hill School.

Career 1999-present: stand-up comedian; 2006: actor in BBC sitcom, Extras; 1993-1997: actor in BBC drama series, Grange Hill.

Public life 2013: public face of the WOW petition; winner, Women in Public Life, public affairs achiever award; 2011: winner, Fringe Media Network Award; 2000: winner, the Daily Telegraph Open Mic Award.

Interests Reading, people, planet earth, the universe.