National Crime Agency officers carried out the raids this morning (Tuesday May 11) at locations in London, Surrey, West Yorkshire, and Greater Manchester.
The three men and five women arrested are alleged to be cash couriers responsible for hiding large amounts of cash in luggage on commercial flights to Dubai from Heathrow or Manchester airports.
On each occasion the alleged couriers flew out with large amounts of checked in baggage. Days later they would return with fewer cases.
The investigation began after the seizure of around £1.9 million from outbound passenger Tara Hanlon, 30, from Leeds, at Heathrow in October 2020.
Around a month later Czech national Zdenek Kamaryt, 38, from Ceske Budejovice in the Czech Republic, was intercepted as he attempted to board a flight from Heathrow to Dubai.
A total of £1.3 million cash was found in his bags, with investigators identifying he had made two previous trips in July and August.
Kamaryt pleaded guilty to money laundering offences and was given a two-year jail sentence on 9 March 2021.
NCA senior investigating officer Ian Truby said: “Cash is the lifeblood of organised crime. Organised crime groups need to launder it so they invest it in further criminality.
“Our investigation has identified millions of pounds of what we suspect are criminal profits being flown out of the UK to be laundered.
“What we have seen is huge shipments of cash, with couriers carrying multiple suitcases, with up to half a million pounds in each case. Those couriers would likely have been paid several thousand pounds themselves.
“Our investigation continues, and those arrested today remain in custody for questioning.”