"The Blairs pioneered this strategy and it is a great way of testing the waters," says the leading British literary agent Andrew Lownie. "Mrs Bush is clearly a lot more popular than her husband at the moment and this is a way of serving up a story in a way that is palatable to the public. Longer term, I am sure we will also see a book from her husband and this of course allows for two bites of the cherry. Commercially, it makes great sense. Also, of course, the public tend to mellow in their attitude to even the most hated political leaders over time."