Polygamous marriages, largely confined to Muslim families, are only recognised in Britain if they took place in countries where they are legal.
Currently, any additional wives can receive reduced individual income support, meaning the husband and his first wife are paid up to £111.45.
Subsequent spouses living under the same roof receive around £40. Under the new system of Universal Credit, which comes in next year, polygamous marriages will not be recognised at all.
Ministers pledged to end the ‘absurd’ benefits regime which has seen multiple wives allowed to claim extra welfare payments.
But a House of Commons Library paper has highlighted a loophole in the rules which will allow additional wives to claim a full single person’s allowance, currently worth up to £71, while the original married couple will still get a married couple’s allowance.
The paper said: ‘Treating second and subsequent partners in polygamous relationships as separate claimants could mean that polygamous households receive more under Universal Credit than under the current rules.’
The Department for Work and Pensions admitted the loophole but said there were fewer than 50 polygamous families claiming benefits.
The first Asian woman to receive a peerage, Baroness Flather, has spoken out widely on the issue of polygamous families claiming benefits.
‘Under Islamic Sharia law, polygamy is permissible. So a man can return to Pakistan, take another bride and then, in a repetition of the process, bring her to England where they also have children together — obtaining yet more money from the state,’ she wrote in the Mail last year.
‘Because such Islamic multiple-marriages are not recognised in Britain, the women are regarded by the welfare system as single mothers — and are therefore entitled to the full range of lone-parent payments. We cannot continue like this.
‘Why are they allowed to have more than one wife,’ she added.
‘We should prosecute one or two people for bigamy, that would sort it out.’
Currently in the UK it is illegal to marry more than once.
But if the multiple marriages took place abroad then it is not.
A spokesman for the Department for Work and Pensions told MailOnline said that the loophole will exist because extra wives in a polygamous home are treated as single.
‘Polygamy is illegal in this country and it would be wrong for the benefits system to legitimise these arrangements by recognising them in any way,’ they said.