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.
