Around 1,000 men and their illegal multiple wives are thought to be claiming welfare benefits.
The polygamous families could be costing the taxpayer millions of pounds a year by pocketing everything from dole cash to housing costs.
But the Government has said it will not stop the controversial payments until 2013, when it will officially no longer accept group marriages for welfare handouts.
Polygamy is not recognised in Britain but was allowed within the benefits system under the former Labour administration.
Tory MP Philip Hollobone blasted: “I can’t see why we have to wait until 2013 to stop this scandal. Daily Mirror readers will be surprised to find out polygamous marriage, which is illegal, is represented in the benefits system.”
Tory MP Priti Patel added: “This is yet another example of how our system is being abused and this will appal all hard-pressed taxpayers.”
Immigration minister Chris Grayling admitted that he had no idea how many polygamous families are on welfare.
He said they are allowed to claim handouts including income support, housing benefit and child support.
A man and his “first wife” can jointly claim £105.95 in dole payments, made up of a £67.50 single person payout and a couple’s top-up of £38.45. “Subsequent” wives are only entitled to the £38.45 top-up. Mr Grayling added that housing benefit and council tax benefit was “limited to those living in one property”.
A Department for Work and Pensions spokesperson said: “This outdated legislation is in the process of being changed.”
Polygamy is practised by some Muslims and Mormons, and is common in Africa.