LONDON — A former British intelligence officer says he has launched a weeklong hunger strike to show solidarity with Guantanamo detainees, in particular Shaker Aamer.

Aamer is the last U.K. resident at Guantanamo and one of three hunger-striking detainees who lost a bid to stop authorities from force-feeding them. All three have been cleared for release but remain at the prison.

Harry Ferguson — who worked for MI6, Britain's external spy agency — says he is ashamed that an organization he was once proud to be a part of supports detention without trial.

Ferguson wrote on his blog Tuesday that his "energy level dropped to zero" and he felt pain on the first day without food, but that unlike Aamer, he doesn't have to "face the horror" of force feeding.