It is the time of year when the French collectively head off on holiday clutching a few light novels to read on the beach. But this week, as much of the country shut down for a month, the must-have summer read was a book by the French interior minister and presidential hopeful Nicolas Sarkozy.

More political philosophy than pot-boiler, Témoignage (Testimony) is on its fifth print run, bringing the total so far to 275,000 copies. When it went on sale a fortnight ago it sold 55,000 copies in the first week and is now top of the bestseller list in FNAC, a leading chain of bookstores. On Wednesday it was the fourth bestselling book on Amazon (behind two novels and a diet book).

Mr Sarkozy's tome outlines his thoughts on various topics, including his belief that the French need to work harder and be less arrogant. He also recounts his marriage breakdown and subsequent reconciliation with his wife, Cécilia.

Mr Sarkozy, 51, said he brought forward the publication of Témoignage because: "The only time the French talk politics with their family is during the holidays." Ségolène Royal, 52, his expected Socialist rival in the presidential election next spring, plans to publish her political manifesto, Désirs d'Avenir (Desires for the Future) in September.

The publisher Bernard Fixot, the minister's friend, told Le Figaro: "I knew it'd be a success but this has surpassed all my expectations. It's colossal."

"The interior minister has a 50:50 chance of becoming president and people want to know him better, to read a personal book in which he explains who he is and how he works.

"It's not a political manifesto but a kind of 'cards on the table' book."

The French record for a politician's book is held by the former president Valéry Giscard d'Estaing, whose book Démocratie Française, published in 1976, sold nearly a million copies. That did not stop him losing to François Mitterrand in the 1981 presidential election.