George Bush initially believed the only plane not to reach its intended target during the 11 September attacks had been shot down on his orders, according to leaks from the former president's memoir of his two terms in office.

Bush reveals that he gave the order for any further suspected hijacked planes to be shot down after the first aircraft were flown into the World Trade Centre in New York during the 2001 terror attacks.

He at first thought the crash of United Airlines flight 93 in Pennsylvania had resulted from this instruction, although it later emerged that passengers had stormed the cockpit as hijackers flew the plane towards the Capitol building in Washington.

The memoir, Decision Points, is due to be published on 9 November, in the aftermath of the US midterm elections, and Bush is already lined up for interviews on the Oprah Winfrey and NBC Today shows.

The Drudge Report website says the very personal book opens with the line: "It was a simple question: 'Can you remember the last day you didn't have a drink?'" as Bush deals with the well-known issue of his alcohol consumption.

His drinking has previously been said to have come to an end when he woke up with a hangover following his 40th birthday celebrations.

In a chapter about stem cell research, he describes receiving a letter from Nancy Reagan detailing a "wrenching family journey", but says: "I did feel a responsibility to voice my pro-life convictions and lead the country toward what Pope John Paul II called a culture of life."

Bush goes on to describes an emotional July 2001 meeting with the Pope, who had Parkinson's disease, at the pontiff's summer residence.

The Pope reportedly recognised the promise of science but implored Bush to support life in all its forms.

At the pontiff's funeral in 2005, Bush – after a reminder from his wife, Laura, that it was a time to "pray for miracles" – said a prayer for the ABC news anchor Peter Jennings, who had cancer.

The book is said to stay clear of criticising Barack Obama, and a source told the Drudge Report: "You will find the president strong, loving life, and ultimately at peace with the decisions he made."