David Miliband today denied toning down his Labour conference speech to avoid embarrassing Gordon Brown.

The Foreign Secretary was embroiled in the controversy last night after he was overheard by a BBC reporter telling an aide: “I couldn’t have gone any further. It would have been a Heseltine moment.”

Observers had been scrutinising his foreign policy speech for signs of an impending leadership bid but he lavished praise on the Prime Minister from the podium.

The mention of Michael Heseltine is believed to have been a reference to the defeat of Margaret Thatcher in 1990 because MPs assumed that Mr Heseltine was waiting in the wings to take over. Mr Heseltine failed to succeed the prime minister and John Major became party leader.

This morning Mr Miliband told reporters as he arrived at the party conference that the report was hearsay.

“I do not accept any of the allegations that are being put around,” he said. “This hearsay that the BBC is repeating with absolutely no basis is something that they should know better than.”

Mr Miliband is the bookmakers’ favourite to succeed Mr Brown, who will today make the most important speech of his life as he tries to head off attempts to unseat him as Labour leader.

The Prime Minister will insist that he is the best qualified leader to take Britain through the economic crisis. It will be a personal address, setting out the Government’s ambitions for the next ten years. He is to announce proposals to ensure that all school-children in Britain have access to the internet. There are 1.4 million school-age children who live in households with no internet connections.

Under a scheme that will cost £300 million over three years, Mr Brown will unveil an educational technology allowance, by which those households will be given vouchers of up to £700 to pay for broadband connections, technical support and computer equipment. The money will come from the schools and families department’s existing budget and mainly from efficiency savings.

Senior Cabinet ministers are trying to head off early moves by Labour MPs to topple Mr Brown by arguing that he should be allowed until next summer to rescue the party.

They fear an attempt to unseat him, probably involving the resignation of ministers, either when the Commons returns in early October or after the Glenrothes by-election. With Mr Brown preparing to make clear to the Labour conference today his intention to fight the next election, leading Cabinet ministers say that he should be given the chance to turn round party fortunes before next June’s European and local elections.

They believe that voters would not forgive Labour for dropping Mr Brown during a period of economic turmoil, regarding the act as self-indulgent.

If Mr Brown fails to stem the flow of Labour losses next June, however, senior ministers say the case for removing him will be more obvious to the party and more acceptable to the country, and they do not rule out Mr Brown deciding to step down.

The stay of execution would give him the conditions for a more dignified exit. Waiting until next summer would spare Labour the prospect of an early general election, which would almost certainly follow a second change of leader in the same Parliament.

Ministers accept that Mr Brown is having a good conference and expect him to deliver a strong performance with his keynote speech today. They say that the mood of the parliamentary party on the return of the Commons, however, will determine Mr Brown’s short-term future.

Mr Brown is expected to carry out an early reshuffle, possibly at the end of next week, as he tries to keep his critics in line. The conference has been awash with rumours of ministers being sacked.

Some Cabinet ministers fear that the rumblings over Mr Brown will resume in the autumn.

Times Recommends

• The bright side of this winter rain
• Story behind the picture: Snow Leopard, 2008
• Times Charity Appeal: The Place2Be