Revealed: The financial cost of Theresa May’s immigration policy

The UK will lose £850 million over ten years as a result of new visa restrictions on foreign spouses of British citizens, new research suggests.

Analysis of the government's impact assessment from Middlesex University strongly suggests income requirements on foreign spouses could be putting an additional burden on the taxpayer.

"It appears the government got its sums wrong when designing this policy," said Dr Helena Wray, from the School of Law at Middlesex University, who co-authored the research.

"When the cost-benefit calculations for this policy in the impact assessment are properly carried out, the figures actually show that the income requirement could cost the public purse £850 million over ten years.

"It will not reduce the benefits bill; in fact, it is likely to increase it as single people are more likely to claim benefits than those living with a partner."

The government claims the £18,600 income benchmark for brining a foreign spouse into the country was designed to prevent these families becoming a burden on the taxpayer.

Home Office estimates suggested the policy would reduce family visas by 17,800 a year.

Recent figures suggest that guess was, if anything, an underestimate. There has been a 58% drop in overall applications, including an 83.6% drop in the number of visas issued to male partners of a British spouse.

But the research shows that non-EEA foreign spouses, who had the right to work but not to claim benefits, were never a burden on the welfare state.

Researchers pointed out that Home Office statistics only counted the cost of services to migrants but excluded their overall economic contribution, in a move which went directly against the advice of the migration advisory committee. This cooking of the statistics hid the economic effects of the policy, according to analysts.

Government figures also fail to take into account the difference in welfare claims depending on marital status.

Single parents, for example, are more likely to draw on state support if they are alone than if their partner is given the right to work in the UK.

Once a non-EEA partner is in the UK and providing the family with two potential incomes, the family unit is more likely to earn above the cut-off point for welfare.

Critics of the move have also highlighted the severe social effects of the policy, with many families split up by the rules.

Many British people living overseas have discovered they cannot return home with their family, because of the need to show income statements demonstrating they are in work.

Instead they are forced to return home without their spouse and children, find work, and then bring them over.

Others, who have incomes below the £18,600 benchmark, are being forced to live in Europe, which has more family-friendly immigration rules.

A coalition of affected families and charities will take a petition against the policy to Downing Street today, before attending a protest at the Home Office.