A UN housing expert urged the British government today to suspend a flagship welfare reform she said was harming vulnerable people, infuriating a minister who called her findings “a disgrace”.

Grant Shapps said he would write to UN Secretary General Ban Ki-moon to demand an apology and an investigation into the work of Raquel Rolnik, accusing her of "having an axe to grind" and basing her comments on inadequate research. She denied this.

The Conservative-led coalition is implementing welfare cuts it says are crucial to reduce state spending and address what it calls welfare dependency, but this has met fierce resistance.

Ms Rolnik, an unpaid UN investigator, said after a two-week fact-finding tour of Britain that a policy branded the “bedroom tax” by its critics should be suspended and rethought. Officially known as the “removal of the spare room subsidy”, the measure means that social housing tenants deemed to have one or more spare rooms in their homes have since April had their state-funded housing benefits reduced by 14 to 25 per cent.

The government says this is to encourage those people to move to smaller homes, making way for others living in over-crowded homes or languishing on social housing waiting lists.

Ms Rolnik said the measure was punishing people who needed extra space for good reasons. She cited disabled tenants who had adapted their homes to live independently and would lose support networks if they moved, as well as grandmothers who often took in grandchildren whose parents were struggling with addiction. “We are not talking about numbers here ... we are talking about human beings,” she told a news conference in London, adding that people had wept during interviews with her.

Ms Rolnik said that in many places smaller apartments were unavailable due to a dire shortage of social housing.

Her views echoed those of the opposition Labour Party and groups campaigning on housing, poverty or disability who have criticised the measure.

Ms Rolnik's full report is not due until next spring, but a statement and press release outlining her initial findings and recommendations prompted a furious response from Mr Shapps, a former housing minister who is now a minister without portfolio.

“This report is an absolute disgrace,” said Mr Shapps, who is also chairman of the Conservative Party, accusing Ms Rolnik of failing to meet relevant government officials. “She’s clearly got an axe to grind,” he told BBC Radio 4.

Mr Shapps also referred to Ms Rolnik, an architect and urban planner who has held government posts in her native Brazil, as "a woman from Brazil ... a country that has 50 million people in inadequate housing".

Ms Rolnik said she had met officials including from the ministry in charge of welfare, as well as local authorities, social tenants and campaigning groups. She denied that she had any axe to grind, saying that during her research in London, Edinburgh, Glasgow, Belfast and Manchester the bedroom tax had come up again and again as a cause of genuine suffering for the most vulnerable in society. A spokeswoman for Ms Rolnik said that as UN special rapporteur on adequate housing, she asked the British government last year for an invitation to visit and received confirmation in February.

The government says it is unfair for taxpayers, often struggling to afford decent housing in the private sector, to pay for social housing tenants to have spare rooms.