THE UK Government is being challenged by the SNP to prove that Westminster's tough financial restrictions for ­British citizens who want to bring their foreign-born spouses to the UK do not breach human rights legislation.

Immigration changes introduced in 2012 mean that a UK citizen must now earn £18,600 before they can bring a husband, wife or partner from outside the EU to join them in the UK. The income requirement rises to £22,400 for families with a child, and a further £2400 for each extra child.

SNP MEP Alyn Smith, below, has ­condemned the rules as "outrageous" for breaking up families simply because they do not have enough money.

Smith said the policy would particularly hurt Scotland, where nearly half of the population earns below the minimum income requirement.

He also pointed out that women were more likely to be affected, due to the gender pay gap.

Smith, who said he was alerted to the issue by a "heartbreaking" story from a constituent affected by the rule changes, has now ­written to Home Secretary Theresa May demanding to be shown the legal guidance that states the policy is in line with the European Convention on Human Rights provision on the right to family life.

"It seems remarkable that the UK Government thinks that having a family is something that should only be available to the wealthy," he said

"The European Convention on Human Rights (ECHR) clearly outlines that every citizen of the EU has a right to a family life.

"At the very best the UK ­Governments policy is on dubious grounds under the ECHR. I have written to Theresa May, below, asking to see the legal guidance that the UK Government is using to defend the current immigration rules. They clearly discriminate against lower-income families."

Smith added: "Scottish families should not be torn apart to help the Conservative party pander to Ukip's grim anti-immigration rhetoric.

"The heart-breaking story of my constituent who will have their life ruined is the direct result of this.

"Currently, around 60% of Scots support immigration being controlled from Edinburgh, a power that was recommended to be reserved by the Smith Commission.

"This case again illustrates the importance of delivering the power promised to the Scottish Parliament.

"If every country had a policy as backward as this then much of the world's population would be restricted to sharing their lives with only people from their country."

Prior to the change in 2012, British citizens sponsoring a spouse had to prove they had the financial ability to maintain and accommodate their family without "recourse to public funds" - in other words no right to claim benefits - with an income equivalent to about £5,500 a year after tax.

Support from third parties such as family members could also be taken into account - but the changes mean this can no longer be considered.

According to statistics from the Migration Observatory at Oxford University, 48% of people in Scotland in employment would not qualify to bring in a family member on their earnings.

Earlier this year a report by campaign group Migrants' Rights Network concluded that rule changes meant the right to the family life had become a ­"postcode lottery" because of the £18,600 income requirement, due to wage fluctuations across the regions of the UK.

It also pointed out that while the UK Government claimed the tougher rules were to prevent non-EU spouses from being a burden on the UK welfare state, they are already unable to claim most benefits, tax credits or ­housing assistance for at least five years when they arrive in the UK.

A spokesman for the Migrants' Right Network said: "The ­minimum income rule is having an impact and much more so outside of the southeast of the UK, because there is quite a big regional d­iscrepancy between ­average salaries.

"So people in Scotland and Wales tend to be more affected by these rules, as the average earnings are lower. It also affects women more, just because of the [gender] pay gap.

"The minimum wage is about £5000 less than the £18,600 - so we know, for example, care workers are the type of people that are affected by this."

He added: "We are calling for an emergency review of the rules. The minimum wage is there for a reason and everyone who falls through that gap of earning below £18,600 are of course worthy and should be able to enjoy their right to family life in the UK.

"There shouldn't be a choice between leaving the country or not living here with your spouse."

A Home Office spokesman said: "We are building an immigration system that is fair to British citizens and legitimate migrants and tough on those who abuse the system or flout the law.

"We welcome those who wish to make a life in the UK with their family, work hard and make a contribution. But family life must not be established here at the taxpayer's expense.

"To play a full part in British life, family migrants must be able to integrate - that means they must speak our language and pay their way."

A report from the Commons Home Affairs Select Committee has h­ighlighted a series of failures in the UK immigration system, including a rising backlog of ­missing migrants and unresolved immigration cases.

The committee's Labour chairman, Keith Vaz, said: "Our immigration system has left A&E and has entered intensive care."

In response, Prime Minister David Cameron insisted his ­government had addressed some of the problems it had ­inherited from a Labour administration that "let immigration get out of control".