Almost 900,000 unlicensed marriage and baptism ceremonies took place in the 17th and 18th centuries - often inside a prison, new research has revealed.
More than half of all London weddings were taking place in the vicinity of the Fleet Prison in the 1740s, according to the records.
A study of "clandestine" registers between 1667 and 1754 by family history website Ancestry.co.uk, found that London's Fleet Prison was popular for marriages, with disgraced clergymen offering speedy services to anyone willing to pay.
Fleet Prison which is stood on what is Farringdon Street today, was a mecca for 'clandestine weddings' in the 1700s, with people wanting 'quickie' weddings for many reasons including speeding up inheritance processes or because of an accidental prenuptial pregnancy.
The government passed the Hardwicke Act of 1753 to end this underground marriage trade.
Miriam Silverman, UK content manager, from Ancestry.co.uk, said:
By choosing to take their vows outside the institution of the church, many of these 17th century clandestine weddings were shrouded in secrecy.
These historic records have been digitised and published online for the first time with the originals held at the National Archive.