Rushed out in under three weeks, Nicolas Sarkozy's new book "A Prisoner's Diary" has plenty of colour about what it's like for a former president to find himself in the isolation wing of a French jail.

We learn that prisoner number 320535 had a 12 square metre cell, equipped with a bed, desk, fridge, shower and television. There was a window, but the view was blocked by a massive plastic panel placed outside.

"It was clean and light enough," writes Sarkozy. "One could almost have thought one was in a bottom-of-the-range hotel – were it not for the reinforced door with an eye-hole for the prison guards to look through."

Sarkozy, 70, was released from La Santé prison in Paris last month after serving 20 days of a five-year jail sentence for taking part in an election campaign funding conspiracy. This is his 216-page memoir.

Told he would have to spend 23 hours out of 24 in his room – and that contact with anyone other than a prison employee was forbidden – the former president chose not to take the option of a daily walk in the yard, "more like a cage than a place of promenade".