The number of suspected sham marriages by illegal immigrants has leapt by more than half in the past year.
Home Office figures for 2009 show a 54% jump, with 529 suspected cases reported by registrars in England and Wales.
The leap comes after the Law Lords overturned a government scheme designed to stop illegal immigrants marrying.
Registrars have told the BBC that marriage rackets are using Eastern European brides to provide other migrants with a toehold in the UK.
The scale of the problem has been highlighted in a special BBC investigation in which a reporter posed as an illegal immigrant - and quickly found people offering to help him marry.
In 2005, the government told foreigners they needed the home secretary's permission to get married in the UK. If someone did not have a legal right to be in the country, they were denied a certificate of approval.
Registrars had lobbied for the change saying they had been powerless to stop a massive rise in bogus marriages, with more than 3,500 suspected cases in one year alone.
Within months of the introduction of the home secretary's veto, the number of cases dropped dramatically.
But the Law Lords later said the approval scheme breached human rights because it unfairly affected almost every foreign national, without trying to work out whether a couple were conning the system or not.
The latest Home Office figures show that in 2008, the last year the scheme was in force, registrars reported 344 marriages to the home secretary for further investigation.
In the 11 months to the end of November last year, the number of suspected cases went up by more than half to 529.
Registrars have told the BBC that sham marriage rackets have returned and many are using Eastern European spouses who have a legal right to be in the UK. This makes it easier for the migrant from another part of the world to settle.
Mark Rimmer, the superintendent registrar for the London Borough of Brent, said: "The government legislated to address the issue and were very successful.
"If nothing is done, I think we will go back to where we were. We had people queuing up in our waiting area - all of them were just bogus marriage after bogus marriage."
Investigation: Bogus brides for illegal migrants
Mr Rimmer said registrars were seeing cases where the couple could not speak each other's language and their body language made it obvious that they barely knew each other.
"Pakistani and Portuguese is one that has seemed to crop up recently. If you see one [couple] that's OK. But when you see three in a week, you start to think that something strange is going on."
Immigration minister Phil Woolas said the government regretted the Law Lords' ruling and was looking again at the law.
But he added: "Just because someone is married does not mean at all that their immigration status is granted.
"The registrars have a system of reporting where they think a marriage is not genuine. Those reports are then used by the immigration officials. The issue of marriage is different to immigration status. A visa will not be issued if there is reason to think the marriage is not genuine."
The government is considering whether to introduce new methods of controlling marriages involving foreign nationals, including the introduction of biometric checks.