Universal credit is to be phased in by 2021

That amounts to £317.83 a month for each wife in polygamous household

Polygamous marriages are only recognised in Britain if they took place in countries where they are legal

Men with more than one wife will qualify for extra benefits under the new welfare system, according to official House of Commons research.

Under the universal credit welfare system, which is not expected to be fully introduced until 2021, polygamous households will be rewarded with higher benefits, The Sunday Times reports.

In the UK, it is illegal to marry more than one person.

Polygamous marriages, largely confined to Muslim families, are only recognised in Britain if they took place in countries where they are legal, such as Middle Eastern states, Pakistan and Zambia.

There no official figures but it is estimated that there may be as many as 20,000 polygamous marriages in the British Muslim community.

Currently, a husband and his first wife are paid up to £114.85 a week. Subsequent spouses living under the same roof receive around £40 each.

Under the new system of Universal Credit, which is not expected to be fully introduced until 2021, polygamous marriages will not be recognised at all.

The standard allowance is about £498.89 a month for couples, but single people can claim about £317.83.

That means the husband and his first wife will be able to claim the married couples' allowance and subsequent wives will be able to claim a single person's allowance.

A briefing paper by the House of Commons library read:

'The 2010 Government decided that the UC [Universal Credit] rules will not recognise additional partners in polygamous relationships.'

'This could potentially result in some polygamous households receiving more under UC than under the current benefit and tax credit system.'

It pointed out that a wife in a polygamous marriage 'does not generally have the right to a state pension on the basis of her spouse's contributions'.

Philip Hollobone, Tory MP for Kettering, said the government should ensure that such households are not rewarded.

'[Polygamous marriage] is illegal and should be prosecuted as such, and there should be no advantage to polygamy through the pensions and benefits system,' he said.