Polygamous marriages, largely confined to Muslim families, are recognised in Britain only if they took place in countries where they are legal.
At present additional wives can receive reduced individual income support, meaning the husband and his first wife receive up to £114.85. Subsequent spouses living under the same roof receive a reduced allowance of about £40 each.
Under the new system of universal credit, polygamous marriages are not recognised at all.
But a House of Commons library paper, published earlier this month, has highlighted a loophole that will allow additional wives to claim a full single person’s allowance while the husband and his first wife still receive theirs.