The restless neighbour: Brown fears entering No 10 in four years' time - just as voters fall out of love with Labour

Thursday was a night of mixed emotions for Gordon Brown. He was delighted to learn that two close allies and fellow ministers, Alistair Darling and Nigel Griffiths, held their potentially tricky seats in Edinburgh. But he knew that Labour was performing worse than he hoped across Britain as a whole.

"I promise we will listen and learn," Mr Brown said after winning his Kirkcaldy and Cowdenbeath seat. Intriguingly, Mr Blair used very similar words outside No 10 yesterday, saying: "I have listened and I've learnt."

A sign that the two architects of New Labour think like twins after reforming their partnership during the election? Or a sign that Mr Brown is already calling the shots?

Whatever the answer, there is no doubt that the election leaves the Prime Minister-long-in-waiting closer than ever to inheriting the crown. While Mr Blair's allies claim he could still serve another three and a half years in Downing Street, Mr Brown's supporters envisage a much shorter tenancy.

Yet there was little jubilation, even among the Chancellor's most loyal acolytes. The result may well speed up his short move through the connecting door that links No 10 and No 11, but it also raises the prospect that Mr Brown has feared since he stood aside to give Mr Blair a clear run at the Labour leadership in 1994: that he will take over as Prime Minister at the fag end of a Labour administration which has run out of steam, time and voter affection.

The Chancellor, who received an ecstatic reception from Treasury officials yesterday, has a long list of new policies, fresh ideas and even constitutional changes in his bottom drawer. But he will now be fretting that a change of leadership may come too late for him to win a fourth successive term for Labour.

Mr Blair, who was once Mr Brown's junior partner, would be the man who won a hat-trick of election victories, while he would be the man who merely played one, lost one.

Allies say Mr Brown deserves a chance to make his mark. They believe that being Prime Minister for a year before the next election will not be enough, since Labour's reduced majority makes a hung parliament a real possibility in 2009.

They would like Mr Blair to stand aside much sooner than the three and a half years he intends to serve, perhaps as early as next year, after the planned referendum on the European Union constitution.

Despite the convincing show of unity the two men put on during the election, there were some signs of tension yesterday between their respective supporters over the timetable for the succession.

"There should be a one-year period of transition," said one Brownite MP. "Tony must realise that the election would have been a complete disaster without Gordon at his side."

As the Commons rebellions on university tuition fees showed, Mr Brown's backbench allies can cause headaches aplenty for Mr Blair. Another Brown admirer said: "Tony is not going to get the reforms through that he will want - even if all the Brownites support him. Gordon has got a complete lock on the process."

Not surprisingly, that is not how Team Blair sees it. "He has got Gordon over a barrel," one ultra-Blairite MP claimed. "The moment Tony withdraws the New Labour imprimatur from Gordon, he will be in trouble.

"He wouldn't get the blessing of the electorate - and Rupert Murdoch - without Tony's support. Gordon can become Prime Minister, but he will need Tony if he is to succeed as Prime Minister."

Another Blair admirer put it more bluntly: "Tony needed Gordon for the election. But it's over, and he doesn't need Gordon as much now."

It seems pretty futile to argue about who needs whom most. What the election showed is that Labour needs both of them to work closely together.