Harems of migrants to be banned.
They will be allowed only one wife and must provide documentary proof they have divorced all other spouses when applying to settle here.
The new rules were issued by Immigration Minister Phil Woolas, who said: "Just because people come from a different culture it does not mean they can usurp UK immigration law."
Up until now migrants' polygamous marriages were recognised in Britain provided the weddings were legal in the countries where they took place - with extra wives able to claim income support benefits at a special rate of pounds 36.65 a week.
There are thought to be 1,000 harems in Britain costing at least pounds 5million a year but the rules will see dozens more turned away.