A United Nations official has refused to back down over criticism of the so-called "bedroom tax" after calls from Tory chairman Grant Shapps for her to apologise.

Raquel Rolnik, the UN special rapporteur on housing, stood by her attack on the policy which she said was causing "great stress and anxiety" to "very vulnerable" people.

She insisted that her visit to inspect housing in the UK had been on the invitation of the Government and said she had met English housing minister Don Foster and English communities secretary Eric Pickles during her stay.

Ms Rolnik's unprecedented inspection has taken in trips to Edinburgh, Glasgow, London, Belfast and Manchester where she has spoken to people on housing estates and at food banks.

She said some tenants were contemplating suicide due to the changes, adding that the bedroom tax could constitute a breach of human rights laws.

"The right to housing is not about a roof anywhere, at any cost, without any social ties," she said in a news conference in central London to publicise her inspection's preliminary findings.

"It is not about reshuffling people according to a snapshot of the number of bedrooms at a given night.

"It is about enabling environments for people to maintain their family and community bonds, their local schools, work places and health services allowing them to exercise other rights, like education, work, food and health."

She added that she had been "deeply touched" by the testimonies she had heard from people affected by the policy including single parents and grandparents who look after grandchildren in their homes.

She said "many people" were increasingly having to choose between food and having to pay the "penalty."

Ms Rolnik's remarks come after Mr Shapps said he had written to UN secretary general Ban Ki Moon demanding an apology and explanation for her "disgraceful" comments.

He insisted the UN investigator had not been invited to Britain by ministers, and was biased.

"She has clearly come over with an agenda," he told BBC Radio.

"It is completely wrong and an abuse of the process for somebody to come over, to fail to meet with Government ministers, to fail to meet with the department responsible, to produce a press release two weeks after coming, even though the report is not due out until next spring, and even to fail to refer to the policy properly throughout the report.

"That is why I am writing to the secretary general today to ask for an apology and an investigation as to how this came about."

Speaking at the news conference, Ms Rolnik said Britain's previously good record on housing was being eroded by a failure to provide sufficient quantities of affordable housing as well as some aspects of the welfare reform programme, including the "bedroom tax".

"Housing deprivation is worsening in the UK," she said.

"Increasingly, people appear to be facing difficulties accessing adequate, affordable, well-located and secure housing."

She said the "bedroom tax" was an "especially worrisome" aspect of the recent welfare reforms.

"I would suggest that the so-called bedroom tax be suspended immediately and be fully re-evaluated in the light of the evidence of its impact on the right to adequate housing and general well-being of many vulnerable individuals."

Under the Government's welfare reform, social tenants deemed to have more bedrooms than they need have had their housing benefit reduced since April.

Ministers say private sector renters do not get spare rooms for free, and argue the change will save around £500 million annually.

However, it has sparked protests across the country with opponents claiming it is forcing families into poverty and will increase the benefits bill by pushing people into the private sector.

Ms Rolnik's final report will be presented in Geneva to the UN Human Rights Council in March next year.

Scottish housing minister Margaret Burgess welcomed the findings. Ms Burgess said: "The bedroom tax is unfair, ill-conceived and risks pushing people to the edge and we have made clear that following a vote for independence this policy will be scrapped.

"It is significant to see that the UN special rapporteur has come to the same conclusion as the Scottish Government on the UK Government's bedroom tax, describing it as a detrimental measure which has serious impacts on the most vulnerable of our society.

"The Scottish Government, like the UN Special Rapporteur, takes the view that an approach to housing challenges which puts the needs of individuals and communities, as well as the principles of equality and respect for human rights at the heart of public policy decisions, is the right way forward."