A statement from the French coastguard, said that late on Friday, the Regional Operational Centre for Surveillance and Rescue Jobourg was informed of a patient on board the ship, which was off the coast of La Hague, parallel to Alderney.
It set up a conference call between the ferry and clinicians in Tolouse, who advised immediate evacuation.
A French Navy Caiman helicopter, with a medical team on board, was sent to rendezvous with the Clipper where members of the team were dropped aboard to help evacuate the patient, who was airlifted to Cherbourg and transferred to hospital.
Ferry passenger John Quayle was woken up by a tannoy announcement at about 1am, asking for assistance from a doctor or nurse.
‘A little while after the first calls the captain himself made an announcement that "we have a medical emergency – the patient is stable but needs to be evacuated to hospital, so the coastguard helicopter will be overhead in 10 minutes",’ he said.
‘We were told to stay off the decks during the operation.’
Mr Quayle, who used to work in aviation, believed the ship kept moving while the medical evacuation took place, but may have turned into the wind.
‘Ships being winched from do not stop, it actually helps the helicopter if it keeps moving – safer in the event of an engine failure on the helicopter.
'It was very noisy in the cabins when the helicopter was in the hover overhead, for perhaps 10-15 minutes.’
Mr Quayle added at breakfast, shortly before arriving three hours late into Portsmouth, a further tannoy announcement asked for two nurses travelling as passengers who had assisted the patient during the night to come forward to receive a gift from Condor.
A Condor Ferries’ spokesman thanked the Clipper’s crew, who he said acted swiftly and professionally to help the stricken passenger.
‘They are trained to deal with these incidents and it is imperative that medical assistance is administered as soon as possible,’ he said.
‘We are grateful to the two nurses travelling on board who volunteered to help and our best wishes are with the gentleman who fell ill. We apologise to passengers who were delayed as a result of this incident.’
No details on the patient's identity or condition has been released.