Britons who were on a mercy mission to Gaza told today how it had been forcibly stopped by the Israelis.
Six Britons flew into London's Heathrow Airport telling how their boat had been boarded by the Israeli authorities.
The Free Gaza movement said that, following their time in custody, they had been deported.
They were among 21 crew and passengers of varying nationalities on the Spirit of Humanity who were held last week.
Adie Mormech, 31, a human rights worker from Rusholme, Manchester, said: "We left from Cyprus. There have been five successful voyages before when we have brought medical supplies and toys into Gaza.
"Israel won't let us go by more conventional means - there is a blockade, which is completely illegal."
Alex Harrison, 31, a full-time activist, from Islington, north London, whose husband is a Palestinian, said: "They towed the boat around in the sea with violent force, making everybody seasick, and confiscated our equipment.
"We spent time in army custody and in prison, then, last night, we were told we were being moved."
Mr Mormech added: "The boat is still there. We and the Cypriot authorities are working hard to get it back.
"The voyages will continue, we will keep challenging the blockade."
The activists said they had set off from Cyprus last Monday and their boat was boarded the next day.
Hilary Smith, a volunteer with the Free Gaza movement, who has been working in Britain to help resolve the affair, said the voyage was to raise awareness of the blockade and to challenge it.
As far as the movement is concerned, we are not going to stop challenging the siege," she said.
"We have had five successful voyages and now three that have been stopped, including this one."
The Britons who were deported, she said, were Ms Harrison and Mr Mormech, plus a postal worker, Theresa McDermott, 42, from Edinburgh, an activist, Fathi Jaoudi, from London, the boat captain, Denis Healey, originally from Portsmouth and now living in Cyprus and the documentary filmmaker, Ishmahil Blagrove.