The owner of a London bureau de change and two of his employees have been jailed for laundering more than £100 million of criminal cash through their central London branches.

Southwark crown court heard how the men’s underworld contacts would queue with unsuspecting tourists to exchange bags of “dirty” money, including cash from drug deals, for “clean” €500 notes — used because they were easy to conceal.

Thillianathan Kumarathas and Ramanathan Thayaparan recruited Dinesh Kumar Anandan into their money laundering enterprise at two branches of Premier Exchange in Victoria.

The three defendants were thought to have taken a cut of up to three per cent per transaction between 2005 and 2009. Their money-laundering service was discovered by HM Revenue and Customs during an investigation into two London cocaine traffickers.

The three men invested the money in properties in the UK, France and India.

Kumarathas and Thayaparan also used it to pay for their children’s private school fees.

Other investments seized by HMRC officers included cars, restaurants and supermarkets, plus more than £80,000 cash from raids at the two branches and the men’s homes.

Thayaparan was employed as a money laundering reporting officer with the job of alerting the authorities to criminal transactions.

On Friday, Kumarathas, 58, and Thayaparan, 42, both from Harrow, were jailed for nine years and five years respectively.

Anandan, 42, from Enfield, was sentenced to two years in prison.

The men were found guilty of money laundering offences under the Proceeds of Crime Act 2002.

David Margree, assistant director of HM Revenue and Customs, said: “This was a calculated attempt to make a dishonest living and help organised criminals go undetected by exchanging the money they got from criminal activity.”

British money exchanges stopped selling €500 notes in 2010 because they were used by money launderers. The Serious and Organised Crime Agency had estimated that 90 per cent of the notes in circulation were held by criminals.

While £1 million in £20 notes weighs 50kg, the equivalent in euros weighs just over 2kg — and one cereal box could hold €300,000, making the notes easier to smuggle.