Media playback is unsupported on your device Media caption The Briton who married an American and moved to France to get into the UK

British citizens are bypassing immigration regulations to get their relatives into the UK, using a technicality that means that if they work in another European country for three months, they can be considered under EU rather than British law on their return. Is this cheating the system or just getting past unfair rules?

Sarah Pitard is a screenwriter from Chicago who had been living in the UK for four years on student visas when she married actor Chris Hall from Swindon, in December 2012.

When the couple applied for their marriage visa the UK Border Agency returned their form saying they had not enclosed payment details. The couple maintain that these details had been included, but by that time it was too late for them to re-apply as Sarah's existing visa was about to expire.

"Our visa was refused and when I calculated how many days I was allowed to stay in the UK it turned out we had 48 hours to leave the country, otherwise I would have been banned for 10 years.

If it is a cheat then we will cheat so that we can stay together for the rest of our lives Chris Hall, with his US wife Sarah Pitard

"I called Chris who had just left for a big theatre tour, and I said 'You gotta come back - meet me at St. Pancras'," Pitard recalls. "And we just shot out on the Eurostar and landed in Paris. I had never even been to France."

Under UK law, Hall was only able to bring his wife, a non-European Economic Area (EEA) citizen, in to Britain if he met the £18,600-a-year base earnings requirement.

But UKBA would not count some of his income as it comes from freelance acting work. So despite being married to a British citizen, Pitard was not allowed back in to the country.

A friend, though, knew of another way of getting a spouse in to the country.

The method they went on to pursue is known as the Surinder Singh route, named after an historic court case. It involves leaving the UK and working in the EEA for about three months.

By exercising your rights under European freedom of movement, your status as a European citizen takes priority over your status as a UK citizen, and when you return to the UK you are allowed to bring your Non-EEA spouse without having to meet the £18,600 minimum earnings requirement which applies to Britons.

In simple terms, EEA citizens have stronger migration rights than UK citizens, since they can bring in family members from outside Europe in this way.

"My friend said it's not publicised - it's really hard to find on the UKBA website, you pretty much have to know about it in order to find it," Sarah tells me. "They don't make it easy because they don't really want anyone to know about it."

It is therefore easier for someone from France or Germany living in the UK to bring in their Indian or American partner or relative, and each year around 20,000 non-European family members come into the UK this way.

Sonel Mehta, of Reading, is currently living and working in Dublin in order to bring her parents across from Australia. They were blocked from moving to the UK by new rules on dependent relatives introduced in July 2012.

"It's the only route that's open to us and I think it's left open because the government can't close it," Metha says.

Image caption In migration terms EEA citizens have stronger rights than UK citizens

Although she knows the route is completely legitimate, she is expecting trouble when she arrives in the UK with her parents and tells the Border Agency official that she is using the Surinder Singh route.

"It will be clear that my parents are coming to settle in the UK. I'm absolutely expecting questions. I'm expecting the immigration officers to deny my right to be able to do that, but I'll have all the evidence with me to show that I have exercised my treaty rights in Ireland," Metha explains. "And paperwork printed out from the UKBA website which says that this route is something that British citizens can avail of."

Guy Taylor, of the Joint Council for the Welfare of Immigrants, says that as other immigration options are closed off an increasing number of people are using the Surinder Singh route.

"One person I spoke to yesterday is working in an arcade in the south of Germany with his Russian wife," Taylor says.

"There are people who are working in Portugal, Spain, France. A lot of people going to Dublin - obviously because of the language.

"It's hard to estimate exactly how many people are doing this because so many don't declare they're going. There are Facebook groups about people trying to share flats and actually co-ordinating on this."

But he added that a whole new group of people are now falling foul of immigration rules.

"For the first time, we're seeing immigration rules hitting white British people and there's a lot of anger about that because this is an infringement on British people's rights, not just about immigrants."

But David Goodhart, director of think-tank Demos and author of The British Dream, a book about post-war immigration, believes the Surinder Singh route should be closed.

"I would regard that as a loophole. When different European countries are trying to place restrictions on the number of people coming from outside Europe, it seems bizarre that those people who are not British citizens find it easier to bring people in from outside the EU than British citizens," he says.

"To have rules about controlling people coming into the country from outside Europe, just made fun of by a European regulation - it should be stopped."

Media playback is unsupported on your device Media caption Watch the Newsnight film in full here

The Immigration Minister Mark Harper declined to be interviewed for BBC Asian Network/Newsnight's report and instead issued a statement:

"The EEA family permit is not a 'loophole'. It reflects the current requirements of EU law and would not apply if someone went abroad to a member state for a short time just in order to circumvent the immigration rules. An application will be refused if it cannot be proved the British citizen was genuinely engaged in employment."

This somewhat contradicts the UKBA website which says that it does not matter if the only reason a British national goes to another member state is to exercise an economic Treaty right so that they can come back to the UK with their family members.

Those using the route argue they have been forced into a corner. In Paris, Chris Hall says he is not in the least ashamed.

"We're doing this because we have no other options. So we're going to go ahead with it and if it is a cheat then we will cheat so that we can stay together for the rest of our lives."

Listen to Catrin Nye's documentary at 17:00 BST on the BBC Asian Network and see the film at 22:30 BST on Newsnight on BBC Two, both on Tuesday 25 June 2013.