A documentary following a covert police operation hunting sex traffickers which began in Cirencester will air its penultimate episode tomorrow.

Taken: Hunting the Sex Traffickers follows the South West Regional Organised Crime Unit over three years as they investigate a brothel run by a Cheltenham human trafficker.

The investigation started after an anonymous letter was delivered to Cirencester police station accusing two men of trafficking women from Brazil to illegal UK brothels.

The three part, fly-on-the-wall series is the first time the dedicated police unit has allowed cameras to film its secret investigation into a human trafficking gang.

With access to a range of secret tactics, from large-scale surveillance teams to undercover officers, this unit used every tool in the box to work out how the gang operates.

The ultimate target was to bring down its leader, a career criminal who’s always managed to elude the police.

If last week’s opening episode of this startling series didn’t send a shock to your system, the second edition on Monday at 9pm will.

The covert police unit visits brothels to meet the women being exploited. What they recount is shocking but none of them will give evidence.

To bring down an organised crime boss, he needs to be caught red handed.

Having secured the intelligence, the police unit must now get the evidence, but this is a man who’s spent his whole life avoiding the long arm of the law.

Taken: Hunting the Sex Traffickers can be watched on Channel 4.