Campaigners will protest outside the London offices of private security firm G4S tomorrow over its role in the illegal detention of Palestinians in Israeli jails.
G4S holds contracts to equip jails in which Palestinian political prisoners, including children, are held without charge or trial in "administrative detention."
Campaigners said such imprisonment breaks international rules on the right to a fair trial, including the Fourth Geneva Convention.
More than 1,600 Palestinian political prisoners staged a mass hunger strike last year and several are keeping up their protest.
Ayman Sharawna and Samer Issawi have rejected food for more than six months, while Yousef Yassin, Jafar Azzidine and Tarek Qa'adan have clocked up two months.
Samer's sister Shireen Issawi, herself a former prisoner, said: "Deliver the voice of the oppressed prisoners and hold this company G4S accountable for its responsibility towards these prisoners and its partnership to the occupation in its inhumane practices."
A G4S spokesman admitted that the company works in Israeli jails.
But he denied involvement with prisons that hold children or people in administrative detention.
Foreign Minister Alistair Burt's admission that the Cameron government has "supported" a survey of attitudes to US drone strikes in Pakistan's tribal areas amounts to a tacit admission of British involvement.