United Nations special rapporteur Raquel Rolnik is charged with assessing whether member states have delivered on the right to adequate housing - a fact-finding mission that is likely to infuriate PM David Cameron.
The PM described Britain in a speech to the UN last year as "a country that keeps its promises to the poorest."
Yet more than 660,000 of the poorest households in Britain are expected to fall into arrears under the coalition policy, with charities warning that around two-thirds are home to someone with a disability.
The scheme cuts social tenants' housing benefits by up to a quarter if the Department for Work and Pensions deems their homes "under-occupied."
Those households, with a median gross income of £209 a week, then rack up an average £728 a year in arrears - the equivalent of six weeks' rent.
If they cannot pay, local authorities and housing associations have threatened eviction - but the authority may decide not to provide even temporary accommodation as failure to pay rent is technically classified as "intentional homelessness."
Ms Rolnik is expected to meet with government officials, NGOs, housing associations and individuals in a tour of England and Scotland.
The Anti-Bedroom Tax and Benefit Justice Federation's Eileen Short said they would be "spelling out in human terms the injustice, insecurity, debt and despair caused by the Bedroom Tax and other benefit cuts."
The arrival follows a 'mass sleep-out' of thousands of demonstrators across Britain on Saturday to highlight a surge in rough sleeping and homelessness if the policy continues.
Greater Manchester Against the Bedroom Tax's Mark Krantz said he hoped many of those at Saturday's sleep-out would come share their own stories with Ms Rolnik and supply written statements for her report.
Mr Krantz showed the Morning Star recent footage of residents preparing to resist an eviction - only to hear from bailiffs over the phone that they were delayed as a tenant in Oldham facing eviction had hanged himself to death.
"To have actually hung himself over the bedroom tax while waiting for eviction - that's unbelievable," he said.