Hampshire Police said magistrates had granted an extension to hold the group for further questioning on suspicion they attempted to hijack the Nave Andromeda.

The seven were arrested on suspicion of "seizing or exercising control of a ship by use of threats or force" and will now remain in custody until Wednesday evening.

After an arrest, officers in England and Wales have 24 hours to question a suspect. A senior officer can then grant an application for a 12-hour extension.

After that, further time has to be approved by the courts up to a maximum of 96 hours.

The Royal Navy's elite Special Boat Service (SBS) was called into action on Sunday evening after the captain of the 42,338-tonne tanker made a mayday call that morning.

In audio of the call relayed in British media, the captain said in heavily accented English: "The stowaways go outside. I see four person port side, midship, near to the manifold.

"And I have two of them starboard side on the bridge... I try to keep them calm but I need immediately, immediately agency assistance."

The Liberian-flagged, Greek-owned vessel had been travelling to Southampton from Lagos, where British police said the stowaways smuggled themselves on board.

Some 16 SBS commandos with assault rifles and night-vision goggles fast-roped onto the deck of the tanker from two helicopters, securing the ship within nine minutes.

Hampshire Police said the seven had made threats to the 22-member crew, forcing them to seek sanctuary in the ship's citadel, from where they raised the alarm.

The vessel, which was six miles (10 kilometres) off the Isle of Wight at the time of the distress call, is now in port in Southampton.