The Labour MP, Vicky Foxcroft, has resigned as a government whip in protest at the government’s welfare plans, saying she will not be able to vote for the cuts to disability payments.

The government is braced for a major rebellion on the welfare bill, which includes significant changes to personal independence payments for disabled people.

Foxcroft, the MP for Lewisham North who was shadow disability minister before the election, said she was unable to do her job as a whip because she disagreed with the changes and did not believe that cuts were part of the solution to rising inactivity.

In a letter to the prime minister, Foxcroft said that the benefits system was “in desperate need of reform” but her experience as shadow disability minister had showed her that the struggles of disabled people and organisations were “even tougher than I had imagined”.

She said: “The last Conservative government left many in poverty and living life in fear of losing their support, not getting access to the right medical care, not having suitable housing and not being able to participate fully in society. The real and ongoing distress was palpable.

“I absolutely understand the need to address the ever-increasing welfare bill in these difficult economic times, but I have always believed this could and should be done by supporting more disabled people into work.

“I do not believe that cuts to personal independence payment (Pip) and the health element of universal credit should be part of the solution.”

Foxcroft, who is among a number of frontbenchers uncomfortable with the proposed changes, said she had wrestled with whether to fight the changes from within the government.

“Sadly it is now seems that we are not going to get the changes I desperately wanted to see. I therefore tender my resignation as I know I will not be able to do the job that is required of me and whip – or indeed vote – for reforms which include cuts to disabled people’s finances,” she said.

“I am incredibly proud to have served as part of the first Labour government in 14 years and hope that ministers will revisit these reforms so that I can continue to support the government in delivering for the people of this country.”