However much he'd like to, Paddy can't come to Tony's party

In the next couple of years, will the phone ring in Ashdown's office summoning him to Downing Street?

SACKED MINISTERS are awkward beasts. Even the saintly Frank Field has been on the warpath in the Sunday newspapers. Imagine, then, the row if Tony Blair had sacked another two or three hard-working Cabinet ministers to make space for Paddy Ashdown and his senior Liberal Democrat colleagues.

He chose not to this time, but the signs are all there that he intends to do so. During Prime Minister's Question Time last week, Tony Benn suggested that while Blair had every right to pick his own Cabinet, he should rule out appointing Paddy Ashdown. Blair refused to do so. His evasiveness prompted The Sun to run a front page story headed "Ashdown to join Blair's Cabinet". Nor was this the first indication of his grand design. Privately, he makes it plain that he sees no difference between his views and those of most of the Liberal Democrat MPs. It is pretty daft, therefore, that they sit on the opposition benches. Publicly, he has declared that he seeks a realignment of the centre left so that the next century belongs to radicals in the same way as this one has been dominated by the Conservatives.

The reason so much speculation surrounds this question at times of reshuffles is that it is the kind of risk that appeals to Blair. On questions of policy he is instinctively cautious and moves slowly, but on the question of how we are governed he likes to live dangerously. Let us not forget that in the midst of all the tentative Green Papers, policy reviews, consultation exercises and experimental schemes being carried out in small corners of Britain where no one will notice, Blair has done more, with devolution in Scotland, Wales and Northern Ireland, to change the constitution in a year than any Prime Minister since the war. And of course, as early as last summer, he established a Cabinet committee with the Liberal Democrats.

To get an insight into Blair's thinking it is useful to return to another exchange between himself and Benn at a Prime Minister's Question session the day after the committee was appointed last July. What was the precedent for this, Benn wanted to know. Blair was not interested in precedent, constitutional conventions or party tradition. "I did it," he declared, "because it is the right thing to do."

Previous Labour Prime Ministers had to take into account the views of trade unions, and the left and right of their parties, before reaching controversial decisions. Blair, unburdened by the weight of party history or sentimental tribalism, took a decision because it seemed obvious and rational. He did it without the support of most of his senior colleagues, with the exception of Peter Mandelson.

Apparently, Gordon Brown went back to his Treasury entourage after hearing the news of the committee and declared dismissively: "You'll never guess what he's done now." John Prescott, normally ultra-loyal in public, said to me shortly afterwards: "There's an agreement with the Liberal Democrats to look at constitutional changes ... He [Blair] wants to do it and he believes in it." Prescott was not remotely tempted to say: "We want to do it and we believe in it."

Blair has already demonstrated a willingness to take on his most senior Cabinet colleagues. So, at some point in the next couple of years, will the phone ring in Ashdown's office summoning him to Downing Street? All that Blair has done suggests he would like to make such a call and all that Ashdown has said suggests he would be delighted to receive it. He admitted last September in an interview in the New Statesman that he had told his colleagues to prepare for a coalition if Labour had failed to get a big majority. But at this point we come to an overlooked problem. It is not Blair's problem, it is Ashdown's.

For, if Ashdown were to receive such a call, he would not be able to say: "Yes." He could only say, rather pathetically: "You know I would like to, but could you hold on for a few days, possibly weeks, while I consult my party." At which point, the explosive manoeuvring becomes highly problematic. Picture a flustered Alastair Campbell emerging from No 10 to tell the assembled journalists and photographers: "The rest of the reshuffle has been delayed while Mr Ashdown discovers whether he can join us."

Liberal Democrats wary of Ashdown's strategy of closer co-operation with Labour have got him in what they call a "triple lock". The deal is that, before any Liberal Democrat can enter the Government, he or she needs the backing of the parliamentary party, a special conference and the membership. As Alan Beith underlined on Sky Television yesterday, Ashdown has to carry the wider party.

Those close to Ashdown insist the consultation could be done very quickly, but not quickly enough for a Prime Minister who knows that the brutal art of reshuffling needs to be accomplished with ruthless brevity. The combination of a prolonged delay, sacked Cabinet ministers roaming the television studios and a sceptical Labour party would be a massive deterrent for Blair. The only way Ashdown could join the Cabinet would be if he were in a position to do so immediately.

The micro-politics of the tense hours in which a reshuffle is held combines with bigger factors to stifle Ashdown's ambition; first and foremost, his his relationship with his party. The view of his closest advisers is that he should have been straighter with them at last year's party conference about the advantages of co-operation with Labour. This September he will be more explicit, which is why Ashdown has predicted euphemistically that it will be a "bit like an old fashioned party conference". There will be a row.

He will succeed in persuading them over time only if electoral reform is established. Witness Lord Steel's remark in this newspaper that "coalition this side of a PR general election is out of the question". But here there are obstacles that will take several years to overcome. Will the party accept the proposals of the Jenkins Commission on electoral reform if they are not fully proportional? How will Blair respond to Jenkins? When will the referendum be held? Can it be won?

In my view, Blair will probably attempt to guide a largely reluctant party towards electoral reform, but even if the referendum is won, a new voting system will not be introduced until after the next election. While all this is happening, he would not want to provoke a backlash by a premature invitation to Ashdown. At the same time, Ashdown's party will not release its triple lock until electoral reform is firmly in place. I suspect the first possible opening for Ashdown to join the Cabinet would be halfway through the next parliament, assuming all goes to plan and Blair is as dominant a Prime Minister as he is now.

So, even though a powerful Prime Minister and a powerful leader seek a closer relationship, they may well find consummation impossible. There are too many hurdles at a time when Ashdown has already been in charge of his party for 10 years. It is more likely that Ashdown will be remembered in the same way as Neil Kinnock: someone who, on a much smaller canvas than Kinnock, changed the course of politics without ever winning the reward of office.