The group, which included 11 couriers and a ringleader, was caught after a year-long investigation by the National Crime Agency (NCA). The couriers flew more than 80 flights, carrying suitcases stuffed with cash and communicating on a Whatsapp group called "Sunshine and Lollipops."

Evidence revealed that around £500,000 was crammed into suitcases that were then packed with coffee granules or sprayed with air freshener to disguise the scent from sniffer dogs. The money was then laundered through a network of shell companies and bank accounts in Dubai.

The ringleader, Abdulla Mohammed Ali Bin Beyat Alfalasi, was jailed for nine years and seven months. The other couriers were sentenced to between two and four years in prison.

The NCA said the case was one of the largest money laundering scams ever recorded in the UK. It said the money was likely to have come from drug trafficking and other criminal activity.

The NCA's head of economic crime, Chris Farrimond, said: "This is a significant victory in our fight against serious and organized crime. These criminals thought they could get away with laundering millions of pounds of dirty money, but we have shown them that they are wrong.

"We will continue to pursue those who seek to profit from crime and bring them to justice."

The case is a reminder of the scale of the problem of money laundering and the need for law enforcement agencies to work together to tackle it.