As Tony Blair prepares to leave Downing Street, it is fascinating to look back to his early days in power and his elaborate mating dance with former Liberal Democrat Leader Paddy Ashdown.

In the months immediately after Labour’s landslide victory in 1997, Blair met Ashdown regularly to talk about a possible coalition government and the introduction of proportional representation for UK general elections. The negotiations continued discussions held during Labour’s years in opposition. Ashdown’s diaries report the talks in minute detail, and are if anything more relevant now, as everyone assesses Blair’s legacy, than they were when published in 2001.

Blair clearly started the talks, in opposition, appreciating the sense of the two progressive parties making common cause. The Prime Minister has never been a tribal politician – that has been the heart of his appeal for the millions who are not wedded to any party – and saw little point in Labour remaining true only to die-hard Labour voters, especially as Neil Kinnock’s failure in 1992 showed the weakness of that approach.

Labour’s extraordinary victory in 1997 changed everything. The fact Blair pursued talk of a Lib-Lab coalition for over a year afterwards underlines his romantic streak: he wanted to create a new progressive alliance despite the fact that raw politics made it impossible. How could a party that had won a 179 seat majority be expected to share power and to change the voting system that had delivered such a huge parliamentary victory? The result would have been Labour MPs voting for their own demise. It could never have happened.

It is fascinating to witness Ashdown’s gradual disillusionment with Blair, and the way hope gives way to despair. Ashdown comes to realise that Blair wants to please everyone, despite the inherent impossibility of doing so. But Blair was obviously committed to achieving some kind of aliance of the centre-left: why else would he have spent so much time as a prime minister with a 179 majority talking to the leader of a party with 46 seats?

Blair comes across as a likeable human being in Ashdown’s diaries, someone at the junction of family life and supreme power in the British state. But Ashdown demonstrates Blair’s inability to grasp the nettle and tell him that the project was dead, a trait that has been repeated on other issues, such as cutting Gordon Brown down to size. How ironic that the PM only really showed iron determination in driving through the decision to go to war in Iraq in support of George W Bush’s presidency.