By Mark White, Home Affairs Correspondent
Up to one in five marriages conducted in civil ceremonies in parts of the country may be bogus, one of Britain's most senior registrars has warned.
In an interview with Sky News, Mark Rimmer, the chairman of the Local Registration Services Association, said 20% of weddings in urban areas were suspicious - the worst it has ever been.
Home Office figures show the number of reported cases has tripled in the last three years to 1,800.
But Mr Rimmer said the number of sham marriages - which were likely an attempt to gain residence in the UK - reported to the authorities was "the tip of the iceberg" and that official figures are a "drop in the ocean" compared with the full scale of the problem.
He said the issue is now worse than in 2004 when the first legislation to combat the phenomenon was introduced and that registrars are having to conduct ceremonies they suspect to be bogus "through gritted teeth".
"We have seen huge increases in potential sham marriages presenting themselves to us, we now have more reports from registrars going to the Home Office, but I think that is the tip of a very large iceberg, and effectively the real scale of the problem is far greater than that that is reported to the Home Office officially.
"Most registration officers are not immigration officers, they came into this business to facilitate marriage. So therefore they don't want to be cynical.
"Unfortunately therefore what happens is the ones that are absolutely blatant get reported and there are some that are borderline that slip through without being reported - and that is the iceberg under the water and that's huge - it is absolutely huge.
"In an area like anywhere in London it is multiple times per week ... it would not be unreasonable to say that 20% of all our marriages are suspicious or have some elements of suspicion about them.
"So one in five in London, probably in the other big cities as well it will be a similar problem. Obviously in county areas in the countryside it is not as big a problem, but certainly in the urban areas, with high areas of ethnicity it is significant."
As part of an investigation into the issue, Sky News witnessed a raid last month by Home Office officials on a suspected sham marriage between a Nigerian man and a Portuguese woman in Harrow, northwest London.
The 32-year-old groom was arrested and has since been deported, while the 22-year-old woman is on bail under criminal investigation.
Cllr Susan Hall, Leader of Harrow Council, said: "It is appalling to see the lengths some people go to in dressing up and organising guests for a sham marriage.
"A marriage is supposed to be the happiest day in your life. Well, in this case, the couple certainly got a day they won't forget."
Mr Rimmer suggested that overall 15,000 of the 173,000 civil weddings that take place each year in England and Wales could be bogus - almost 10 times the official level.
Officials found the process very frustrating, he told Sky News.
"You go into a marriage thinking that you are going to a proper relationship - sealing and cementing someone's relationship - yet you know that this is purely a financial transaction, you can imagine how frustrating that can be. Very often the ceremony is done through gritted teeth," he said.
Sky News joined officials on a raid in September Pic: Dermot Carlin
Both David Cameron and Theresa May have repeatedly pledged to tackle sham marriages.
In a speech in October 2011, Mr Cameron pledged to "end the ridiculous situation where a registrar who knows a marriage is a sham still has to perform the ceremony".
But Mr Rimmer said the situation was worse than ever after a series of legal challenges.
He said: "Sham marriages have been a problem for many, many years. And the previous government introduced legislation to combat it back in 2004.
"As a result of that legislation, it did put a cap on the problem for the first year or so, but unfortunately the legislation was subject to challenge and the government lost on a couple of occasions in the high court.
"Eventually it was watered down to a degree it became meaningless and eventually was repealed in 2010. Since 2010, we have had the problem re-emerging and it is even worse than the problem was in 2004."
In July 2008 the Law Lords ruled that Home Office rules under which foreign nationals needed official permission to marry breached human rights.
Mr Rimmer added that while the rules for British citizens bringing foreign partners into the country to marry have been tightened, EU citizens are still free to abuse the laws.
He said: "The law relating to British nationals getting married is becoming more and more rigid. So therefore there are probationary periods if you marry a British national during which time the Border Agency/Home Office can check up as to whether that relationship is still in existence.
"There is not the same check with European Union nationals, so therefore the scams are usually perpetrated by European nationals other than Brits, because it is more advantageous to do so.
Brodie Clark, former head of the UK Border Agency
"Some nationalities in Europe being trafficked in for the sex industry - are being sold on to go through bogus marriages, so these people are victims in themselves, under duress.
"These sham marriages are a direct result of organised crime, this is organised criminality, a lot of racketeers making millions of pounds out of the racket - this is actually not something that is like a green card - this is massive criminality on an industrial scale."
Mr Rimmer said his organisation is working with ministers to introduce new legislation that could help reduce the number of sham marriages by including ceremonies held in the Church of England.
Brodie Clarke, former head of the UK Border Force, told Sky News it is impossible for officials to police every marriage.
He said: "They can't be everywhere. We do need to depend on the public and have sought that support from registrars to say if there's something suspicious here, please report it. And that would then trigger the attendance of somebody or an examination by somebody from UKBA to look at those circumstances.
"So it can't be done just by uniformed people in the Home Office - it needs partnerships of all. That's the only way this is going to pull together and work.
"But those demands and requirements of partners have to be reasonable and they have to be able to deliver on those demands and requirements - and that's a challenge, I think, for government to make that work."
Immigration Minister Mark Harper told Sky News: "Sham marriages have for too long been an easy target for migrants seeking to circumvent our immigration rules, often assisted by organised criminals.
"Registrars are frustrated when they marry couples who are obviously sham. We need more effective tools to deal with it.
"By extending the marriage and civil partnership notice period to 28 days in England and Wales and allowing this to be increased to 70 days in some circumstances we will make time to investigate, prosecute and remove those involved in sham marriages."
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