A BBC investigation has found that up to £500,000 every week is being spent on prostitution in Northern Ireland.

Police estimate there are 88 brothels in operation, with Northern Ireland having a higher demand for prostitution than most other areas of Europe.

The brothels are usually run by local gangs, including paramilitaries, but there are also foreign groups.

Many of the women working in the brothels have been trafficked from abroad.

They are held captive and forced into prostitution.

The problem is most evident in Belfast, but other towns and cities - such as Londonderry, Antrim, Enniskillen, Portadown and Bangor - are known to have brothels.

The gangs can make millions of pounds in a year by exploiting women they have brought to Northern Ireland illegally.

The PSNI have broken up some of the prostitution rings and rescued dozens of women from the sex trade over the last couple of years.

However, every day, new women are being brought in from abroad and often the women are so traumatised by their experiences they can't help the police bring convictions against the gangs.

PSNI Detective Inspector Douglas Grant said the public needed to know the full extent of the problem.

"There's a significant demand in Northern Ireland for prostitutes and that's larger than other parts of the UK and Europe," he said.