A man from Kosovo was arrested moments before he was due to take part in a suspected "sham" marriage in Blackburn.
Home Office Immigration enforcement officers raided the Register Office, in Northgate, shortly before 15:00 GMT on Friday.
The 29-year-old was found to be in the country illegally. A 20-year-old British woman was interviewed and released.
The groom has been detained pending his removal from the UK.
The operation was carried out with the knowledge of the Superintendent Registrar.
