Mark Rimmer, service director for registrations of marriages at Brent Council, said the number has risen significantly in the past year.

He is concerned that tighter controls on immigration could be persuading more immigrants to take part in bogus unions in an attempt to stay in the UK.

Home Secretary David Blunkett announced in April that new controls were being planned to prevent sham weddings.

'Tougher line'

Mr Rimmer said: "I have been 16 years in Brent and it's the worst I have ever known it.

"It's hard to be exact because we don't have figures, but the problem has increased a lot in the past year.

"You are looking at one in five marriages in London being bogus.

"I think part of the problem is that because the government is taking a tougher line on immigration more people are looking at sham marriages as a way of staying in the UK.

"Whether it's becoming more organised is hard to say."

Mr Blunkett said part of the new proposals may involve foreign nationals who want to marry going to a special register office where they would be subject to immigration checks.