Alexander Mitchell, 44, spent over a year in solitary confinement. He told British media he confessed under torture, fearing for his life. He was found guilty by Saudi authorities and told he would be crucified.
"When I arrived in the detention centre they told me: 'You will confess or you will go insane with what we're going to do to you'," he told BBC Scotland.
"I was kept awake for nine days, chained to the door of my cell so I could not sleep or sit down," the Guardian newspaper quoted Mitchell as saying.
"In the evening times I was hooded, taken upstairs in chains to one of the interrogation rooms, where the beatings then progressed to torture. The beatings started with punching, kicking, spitting and eventually progressed to hitting me with sticks."
Near breaking point
Mitchell told the BBC he had been beaten on the soles of his feet with an axe handle, adding: "It went on and on.... I used to consider myself a strong person but everybody has their breaking point. I was alone and in pain, and if it wasn’t me being beaten it was others and I could hear their screams."
"I expected to be beheaded and crucified at any time."
The men were said by the Saudi authorities to have been alcohol smugglers who used bombs between November 2000 and March 2001 to attack rival bootleggers in the strict Muslim kingdom, where alcohol is banned.
But their families and lawyers said they were scapegoats for bombings carried out by Muslim groups which killed one Briton and wounded three other Westerners.
Mitchell and Canadian, William Sampson had faced execution for the car bomb that killed British national Christopher Rodway.
Saudi authorities have denied any mistreatment.
The BBC quoted the Saudi embassy in London as saying the men had stayed in air-conditioned rooms with regular access to visitors, lawyers, exercise facilities and whatever food they asked for.
Saudi foreign affairs advisor Adil al-Jubair said on 17 August the Riyadh authorities had proof against the men and stood by it, the paper said.
"For people to think Saudi Arabia tried to pin charges on foreigners in order to hide a terrorism problem is preposterous," al-Jubair said.
According to a tally of official statements, Saudi Arabia has executed 38 people this year.