Sri Lanka says it is sending 21 containers of recycled waste back to the UK after they were found to contain hazardous material.
Customs officials said hospital waste, plastic and polythene was discovered in the majority of the 263 containers imported in 2017 by a private firm.
The shipment was meant to be made up of used mattresses, carpets and rugs.
Most of the containers have been stored in warehouses, with only a small amount of material having been re-exported.
Legal action was taken after the Sri Lanka authorities impounded the material in 2018.
Officials said the 21 containers had left Sri Lanka on Saturday.
Customs spokesman Sunil Jayaratne said the original importation breached international and EU rules and regulations on hazardous waste and its disposal.
England’s Environment Agency said it was committed to tackling illegal waste exports.
An EA spokesperson said: “We are in contact with the Sri Lankan authorities and have requested more information which would allow us to launch a formal investigation.”
Several other countries in the region have recently begun to return waste imported from foreign countries.
In January, Malaysia returned 42 shipping containers of illegally imported plastic waste to the UK.