One of Gordon Brown’s closest allies left open the option of an autumn election yesterday but spoke of the “big job” still ahead of the Prime Minister to convince voters that he could deliver changes in schools, hospitals and affordable homes.

The intervention, by Ed Miliband, follows the leak of a memorandum sent to Mr Brown by one of Labour’s best-known polling experts advising him to consolidate his grip on power by calling an early election after “a short period of intense and compelling activity”.

The memo from Philip Gould, who was Tony Blair’s polling adviser and an architect of new Labour, bears a striking similarity to the strategy followed by the new Prime Minister in his first weeks in Downing Street.

Lord Gould of Brookwood advises him that the political landscape is changing, with security the main issue for voters preoccupied with crime, terrorism and immigration, ahead of Labour’s previous priorities of economic competence and public services.

“You should position yourself as a powerful, muscular modernisation politician with the power and the determination to change Britain. You should aim to be a great reforming PM,” says his memo, which was leaked to the Daily Mirror.

He urges Mr Brown to begin election planning early and to reject a strategy of consolidating his Commons majority, saying the risks of any swing to the Conservatives are too risky.

The release of the memo has irritated Mr Brown’s inner circle. One suggested that the pollster was disappointed not to have been invited to the Prime Minister’s first political Cabinet a week ago.

Mr Miliband, the Cabinet Office Minister whom Mr Brown put in charge of drafting Labour’s next election manifesto, tried to play down its significance, suggesting that it was written in the aftermath of the 2005 general election before the timing of Mr Blair’s departure was settled.

“I gather it was written a couple of years ago,” he told The World at One, on BBC Radio 4. “I certainly do not remember it being discussed in the transition planning.”

He said that the manifesto would be ready whenever it was necessary. While he would not rule out an election this year, he indicated that Mr Brown wanted time to prove himself to voters first.

“We’ve got a big job to do to earn people’s trust and show that on the issues that matter – housing, health and education – we can make the changes that people really want to see,” he said.

Lord Gould is not a formal polling adviser to Mr Brown. His counterpart in the new No 10 regime is Deborah Mattinson. She set out her own analysis a fortnight ago, arguing that David Cameron had misread the mood of voters, which was “sober and reflective” at a time when the Conservative leader was offering “showbiz and razzmatazz”. She said that people welcomed Mr Brown’s purposeful and focused style of leadership.

“These leadership qualities – strength, experience and conviction – match the popular mood and chime with people’s sense of what matters for a Prime Minister,” she wrote in The Sunday Times.

Senior Conservative strategists believe that Mr Brown will decide not to hold an election this autumn, pointing out that Labour is behind in the polls in Scotland where the party has 39 seats. The Tories are, nevertheless, stepping up their own preparations.

“We have always thought that Brown might go this autumn and have been working with that in mind,” said one of Mr Cameron’s election chiefs.

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