Steve Richards: This is the reason why we should all be interested in the saga of Blair and Brown

Blair's implicit message is: 'That guy next door cannot be trusted with the top job'

Here is a conversation I had with some friends on Sunday. We were reading the newspapers and one of them looked up to state despairingly: "I do not want to read another word about the relationship between Blair and Brown". Almost certainly my friend spoke for Britain and, to be slightly more parochial, the readers of The Independent. Nonetheless I looked up from the newspaper I was reading to reply with a grim-faced sense of duty: "Well, I will probably be writing about the relationship tomorrow. Sadly it does matter." Once more representing a tired and bored nation my friend asked: "Why does it matter so much?"

Frankly I was not up to rising to the challenge then, having gorged on thousands of words on the subject in those newspapers. But on reflection it is the central question and must be answered. There are reasons for the persistent focus. The relationship, the timing of Blair's departure and the manner in which it takes place are matters of overwhelming importance to the future of the country, the Government and the Labour Party. Here is the answer I should have given my friend on Sunday.

Politicians function in a context. They do not wake up each morning and start afresh. We know Blair is going at some point and that Brown, strengthened by his evident indispensability at the last election, wants to take over as soon as possible. Therefore Blair's determination to continue is in itself a destabilising act. Every day he remains in power, declaring that he has lots to do, is an implicit repudiation of Labour's next prime minister.

I do not criticise Blair for wanting to continue. It is a difficult job to give up at any point, and he has consistently stated he wanted to serve a full term. But he is trapped by the context in which he functions. Given that he has been in the post for more than two terms and Brown is desperate to have a go, Blair's implicit message chimes with the Conservatives' more direct onslaught: "That guy next door cannot be trusted with the top job".

In the meantime Blair's closest allies are becoming increasingly explicit in their disdain for the only feasible successor. In the past fortnight Alan Milburn has attacked publicly Brown's Budget, raised again patronising questions about the Chancellor's "reform credentials" and expressed fears that Brown would move away from what Milburn regards as the centre ground. If they are his public announcements, goodness knows what he has said in private. As the Conservative MP Michael Gove noted on the BBC on Sunday, Milburn "adds credibility" to the Tories' critique of Labour's next leader every time he speaks.

Again it is the wider context that matters. If Labour were blessed with an array of formidable leadership candidates, Milburn's comments would be wholly justified. He would be mapping out an agenda for his own campaign or one for another candidate to adopt. But Milburn does not have the support to stand. Another much-touted potential candidate, David Miliband, does not want the job even if he thought he had a chance of winning, which he does not. So Milburn and a few others seek to destroy the only likely successor.

In Labour's past there would have been more potential candidates. Ironically this would have made Blair's situation incomparably more stable. A larger number of embryonic candidates tend to cling to a current leader in case one of their rivals were to triumph in the event of a sudden vacancy. The prime ministerial careers of Harold Wilson and John Major were extended because there was no single and obvious successor for others to unite around. But New Labour is such a centralised project there are no other power bases within the party. From the beginning Blair and Brown pulled the strings. They are the ones that matter. This is not a healthy state of affairs, but it is the situation that Labour contrived after the nightmare of the 1980s. Looking ahead, therefore, a pivotal objective for the Government and the party must be a unifying transition from one string-puller to the other.

Instead, events and the stifling context in which they erupt undermine what Brown had hoped to achieve as a new prime minister. He had planned to make the restoration of trust a central theme, with reform of the Lords and new constraints on prime ministerial patronage as key policy areas. Now Blair moves on to this agenda in response to the row over party funding. Again the context is crucial. Blair's rushed reforms of the Lords and party funding will lack credibility because they arise out of political desperation rather than as a result of a fresh start under a new leader.

Blair is now in a position where he has to respond to the consequences of his own earlier misjudgements. Every leader makes mistakes. Few are around long enough to face the consequences.

Brown also faces having to deal with the consequences of decisions Blair still wants to take. In theory Blair will make the long-term decisions on pensions, energy and the next spending review. His successors will have to find the money to pay for the outcomes of those decisions. At the moment Milburn is one of those calling for a universal increase in pensions rather than the targeted approach favoured by Brown. Yet already I can hear Millburn complain in a few years' time about tax increases that a Brown government would be forced to introduce in order to pay for the policy.

The more Brown is undermined the less chance he will get to fulfil his prime ministerial potential. I am not misty-eyed about the Brown premiership. It is possible that Milburn and the leadership of the Conservative Party will be proved right and that Brown will alienate Middle England, reform clumsily and prove unable to deal with colleagues. To some extent their persistent onslaught will become a self-fulfilling prophecy.

Yet Brown's extraordinarily long record as shadow Chancellor and Chancellor suggests that he has the potential to be a great social democratic prime minister, a leader that comes along rarely in British politics. Blair says he has lots more to do, but he has had plenty of time already. It is possible that Brown would do better.

Behind the predictable and sometimes self-interested private briefings, the future of the Labour Government and the prospects for the country for the next decade or more are at stake. The Conservatives collapsed in the early 1990s. They have not recovered yet, but will do so at some point. Should one Labour leader be virtually the sole beneficiary of the rare space their collapse has generated, or should another get a chance? In essence that is the question.

Take a deep breath and be prepared to read another hundred thousand words by next Sunday. The timing and context of the soap opera's denouement matter more than any other issue in British politics.

s.richards@independent.co.uk