Couples must give almost twice the official notice of their intention to wed from Monday as part of a crackdown on bogus marriages.
A UK-wide extension from 15 to 28 days was approved by parliament last year in order to allow more time for investigation.
Ministers have made clear they expect registrars to report suspicions to the Home Office, which has new powers to delay nuptials for a further 70 days while inquiries take place.
The changes have already prompted an 80% increase in reports of suspected sham cases – from 1,099 between July and December 2013 to more than 2,000 in the same period last year.
Immigration and security minister James Brokenshire said: “As of today, marriage can no longer be seen as a ‘fast-track option’ for those seeking to abuse marriage to cheat their way into the UK.”
