A couple in their seventies have been detained after about 10kg (22lb) of cocaine was found on a cruise ship returning to the UK from the Caribbean.

Portuguese police said they had detained two people, aged 72 and 70, in Lisbon after information was shared with them by the UK’s National Crime Agency (NCA).

The pair, who are believed to be British, were arrested on suspicion of trafficking narcotics on 4 December when their cruise ship docked in the Portuguese capital. After searching their cabin, police found 9-10kg of the class A drug hidden in four suitcases.

The couple, who have not been named, have appeared before a judge and are being held in custody while a joint Portuguese and British investigation continues.

Portuguese police said: “In the cabin that was occupied by the suspects, four suitcases [were found] in whose structures was concealed a high amount of product, more specifically cocaine.”

An NCA spokesman said the investigation would be led by Portuguese police. They added: “The NCA works with a wide range of international partners and routinely both shares and receives information.”

The couple were travelling on board the Marco Polo, a 425-cabin cruise ship operated by Cruise and Maritime Voyages.

The boat left Tilbury in Essex on 5 November and travelled to the West Indies and Azores with 610 passengers and 294 crew on board. After the pair were arrested, the ship continued on its planned route and returned to the UK on 8 December.

A spokesman for Cruise and Maritime Voyages said: “Portuguese police officials attended the Marco Polo in Lisbon on 4 December and detained two passengers who were travelling on board the Cruise and Maritime Voyages vessel.

“It is understood this was in connection with the suspected possession of narcotics. Cruise and Maritime Voyages is cooperating fully with the Portuguese police officials.” He added that the firm “does not tolerate any criminal activity or anti-social behaviour on board its ships”.