Two men have been jailed for running brothels in Chesterfield, Derby and Lincolnshire.
Meyrick Bramhill-Purchase and Mo Quan Zhou were arrested last May and later charged with seven crimes relating to prostitution and modern slavery.
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Following a 10-week trial, they were found guilty of some of the charges and jailed.
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Zhou, aged 45, of London Road, Derby, has been jailed for five-and-a-half years while Bramhill-Purchase, 64, of Muntjac Way, Witham St Hughs, Lincolnshire,has been handed a four-and-a-half year sentence.
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The investigation, led by the East Midlands Special Operations Unit, with support from Derbyshire Constabulary and Lincolnshire Police, began in May 2015.
That month, a concerned letting agent called Lincolnshire Police to report suspicions that a house in Lincoln was being used as a brothel.
Officers launched an investigation which unearthed evidence of nine brothels - two in Derby, two in Chesterfield and five in Lincoln.
Vulnerable Chinese and Malaysian women were found at the houses, having been trafficked around the country.
A man who visited one brothel in London Road, Derby, called the police when he became concerned that the woman in the house had been trafficked.
Both Bramhill-Purchase and Zhou had rented the properties and paid for adverts on escort websites to attract customers to the brothels.
The brothels typically contained one man, who would act as a minder for the women and who would be responsible for taking money from customers and feeding it back to Bramhill-Purchase and Zhou.
One of these men, Shan Yu, of Uttoxeter Old Road, Derby, was jailed for 10 months last year for his involvement in the prostitution ring.
He admitted controlling prostitution for gain in the city.
Investigators found that the men had sent substantial sums of the money from the brothels abroad, while some had been used to rent the properties.
Inspector Harry Rai said: "Following a 10-week trial, the jury has brought to an end a complex investigation into prostitution and modern slavery.
"These two men were controlling oriental women and operating various brothels in Derbyshire and Lincolnshire for their criminality, which was bringing misery to our communities.
"These women were very vulnerable. Many of them had over-stayed their visas and were desperate to remain in the UK in order to avoid an even worse existence in their home countries.
"This has been a complex investigation into modern slavery and I am pleased both defendants have been found guilty."
Zhou was found guilty of conspiracy to facilitate the travel of another with a view to sexual exploitation, conspiracy to control prostitution for gain, conspiracy to facilitate the travel of another with a view to exploitation, conspiracy to control prostitution for gain and one count of removing criminal property.
Bramhill-Purchase was found guilty of conspiracy to facilitate the travel of another with a view to exploitation, conspiracy to control prostitution for gain and one count of removing criminal property.