ID: Let's start with the coalition. Why do you think a coalition didn't happen with Labour in the end?

TW: I wasn't party to those [post-election] discussions. What I know of these things is that you only get the real story years later. I did have some conversations with Gordon Brown and Ed Balls. They left me in no doubt that there was good intent on their side. Were we organised and prepared for coalition, in terms of a proper structure for negotiation? We weren't prepared. What is interesting is there was clearly a huge level of preparedness on the Conservative and the Lib Dem side for a Lib Dem-Conservative coalition, so they had the advantage. They knew the issues they needed to discuss, and had positions on every issue when they went into negotiations. I suspect our talks were hampered by a lot of shuttle diplomacy as people met and squared off. And let's also be frank, the numbers were harder to put together on a Labour-Lib Dem coalition.

You've said you had an epiphany on coalition politics. What do you mean?

I come from the grassroots of the Labour Party. I joined the Labour Party when I was a teenager. I've been branded a tribal politician all my life, and occasionally have been.

Only occasionally?

Exactly. Only occasionally. The experience of two terms in government as a minister, and particularly for me, my time at the CabinetOffice [2008-2009] - a fascinating department where you see the traffic from all other departments - made me realise that we were in a zero-sum game with some of that stuff. I guess my view of the world was opening up and maturing a little bit.

The expenses scandal was probably the most miserable period for parliamentary democracy of the previous century.

For a year I saw that two-party politics was grinding everyone into a pulp because there was no trust at the centre. Gordon Brown and David Cameron did not have an atom of trust between them.

Had they sat down in a room and worked out a proper reform proposal, not one that gave us IPSA, and actually properly reformed Parliament, we'd be in a better place now. As soon as you see that [lack of trust] up front, you realise you need an apparatus to deal with that. Sometimes coalition can do that.

This is what people outside the Westminster village don't ever get. All political parties are coalitions within themselves. Therefore, you will always have fairly robust policy debates and debates about personalities.

Of course, there are struggles within governments, whether single party or coalition, but the apparatus you put in place to implement those policy differences is absolutely vital. In that sense the likes of Gus O'Donnell [head of the civil service] are often underrated because they allow this conflict resolution to take place on a daily basis without it causing the government to judder.

I got the impression, probably fuelled by a conversation we once had, that you really fell out of love with politics at one point.

I describe it like a magnetic force to me - you can't resist the attraction of it, but at some points in life you are totally repulsed by it. When it's not going your way this political world is a very lonely and solitary life. And then you have great moments when you get change, you can win on a policy issue, and it comes back. So it is a rollercoaster. I suspect there are a lot of MPs who don't admit that to themselves, but it is a magnetic force.

How have you found being in opposition? You seem to have taken to it like a duck to water.

It's revelatory to me to be honest, and I'm deeply embarrassed to admit that I'm really enjoying it. It has moments of fun that government does not give you. It's only moments of fun. There is not a day goes by where I'm not reminded that you can't make the great changes to the country that you can when in power. But you can keep the government honest, and you've got to be quite quick, deft and adept at picking up issues and running with them quickly. You've got to be quite tactical in opposition. For some colleagues who have been ministers before, it does take time to acclimatise.

A Tory MP said to me the other day he thought you'd taken on the mantle of Eric Forth [MP for Bromley and Chislehurst who died in 2006].

Let me know the Tory MP, I'll send him a thank you card. Eric was a great chamber man, a great parliamentarian and he was dogged. I'm not as good in the chamber as Eric Forth was. He was quite brilliant.

Tags: In conversation, Issue 32, Tom Watson