The number of sham marriages reported to the authorities is just "the tip of the iceberg," while official figures are a "drop in the ocean" compared with the full scale of the problem, one of Britain's most senior registrars has warned.
Up to 20% of civil ceremonies in cities could be a sham, Mark Rimmer, the chairman of the Local Registration Services Association, told Sky News.
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Home Office figures show the number of reported cases has tripled in the last three years to 1,800, the broadcaster said.
But in a stark warning Mr Rimmer suggested that overall figure could be nearly 10 times higher, believing 15,000 of the 173,000 civil weddings that take place each year in England and Wales could be bogus.
In cities and urban areas of "ethnicity" one in five marriages are suspicious, he added, with bogus ceremonies taking place "multiple times per week" in London - most likely in an attempt to gain residence in the UK.
"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," he told Sky News.
"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."