Gordon Brown will admit Labour is the underdog but insist it can still win the next General Election - as he asks party members to join “Operation Fightback” at his rally in Coventry this weekend.

The Prime Minister will attempt to reach out to campaigning groups outside the Labour Party, including environmentalists and anti-poverty campaigners, with claims that the Conservative Party hasn’t changed.

He will tell activists: “When you peel away the veneer and actually look at what their policies mean, what you see is it’s not the new economics of the future, it’s the same old conservative economics of the past. They haven’t moved on.”

Mr Brown will also highlight the four key themes of Labour’s manifesto as he effectively launches his election campaign, although he will not officially announce the election.

He is expected to say: “First, we must secure the recovery, not put it at risk. Second, we must support new industries & future jobs.

“Third, while we will reduce the deficit, we must protect and not cut frontline services. Fourth, we must stand up for the many not the few.”

Constituency Labour Parties are to be sent thousands of “operation fightback” packs including magazines, stickers and hints about what to say on the doorstep when canvassing voters.

The West Midlands was chosen for the event because of the high number of key marginal seats where Labour is trying to fight off David Cameron’s Conservative Party, such as Birmingham Edgbaston, Stafford, Redditch, Wolverhampton South West, Dudley South, Nuneaton and Worcester.

Conservatives have defended plans to disrupt the Mr Brown’s rally by encouraging Tory students to turn up and form their own “publicity stunt”.

Members of Conservative Future, the party’s youth wing, have been sent e-mails asking them to turn up at the site of the speech to “act as a demoralising element to Gordon Brown’s trip”.

A party spokesman said: “Conservatives to campaign against Labour? Hardly a big story. Of course we encourage people to campaign against Labour.

“People need to know that the choice at the election will be clear: five more years of Gordon Brown or change with the Conservatives.”

There is speculation at Westminster that the timing of Mr Brown’s speech will detract attention from a series of embarrassing stories about the Prime Minister which are set to be revealed over the weekend.

A book by columnist Andrew Rawnsley is expected to reveal embarrassing details about the Prime Minister’s temper and relationship with staff, and extracts will be published on Sunday.