No more than a few thousand people "stuck" in homes they can not afford will be forced to move because of housing benefit cuts, Iain Duncan Smith has insisted.
The Work and Pensions Secretary accused Labour of telling "a pack of lies" about the potential impact of the reforms - which some have compared to social cleansing.
And he issued a warning to landlords that the "game is over" on high rents, vowing to force those charged to benefits claimants down to commercial levels.
State help for rents is to be capped - at £400 for a four-bed property - as part of an effort to slash £1.8 billion a year from the "out-of-control" housing benefit bill.
Local Housing Allowance rates will also be cut and payments cut by 10% for people who have been on jobseeker's allowance for more than a year in changes that have alarmed anti-poverty groups.
Shadow work and pensions secretary Douglas Alexander this week said the "potentially devastating" reforms risked displacing families and increasing homelessness.
He told MPs London would "look very different in the years ahead" - echoing previous warnings from critics that the less well off would be forced out of the centre of the capital.
Mr Duncan Smith insisted that London Mayor Boris Johnson - who publicly vowed not to accept "Kosovo-style social cleansing" - backed the policy.
"What he said to Labour politicians who were whipping up fear about this - by the way a pack of lies... is that what they were saying, 'social cleansing', is an outrage and is not going to happen," he told BBC1's Andrew Marr Show.
"800,000 living in social housing in central London alone are unaffected by this, this is not Paris."