A website designed to help Muslim men find 'second wives' in the UK has more than 100,000 users.
Polygamy, where a person has more than one spouse, is illegal in the UK, carrying a possible prison sentence of up to seven years.
Such marriages are only recognised if they took place in countries where they are legal.
However, there is no law to stop unregistered religious ceremonies taking place.
Currently, there are more than 25,000 British members using the site.
Azad Chaiwala, from Sunderland, who established SecondWife.com, said he was responding to a need.