Gordon Brown admitted Labour is the underdog but insisted it can still win the next General Election - as he asked party members to join “operation fightback” at a rally in Coventry on Saturday.

The Prime Minister attempted 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, during a visit to Warwick University.

He said: “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 also highlighted the four key themes of Labour’s manifesto as he effectively launched his election campaign, although he did not officially announce the election.

He said: “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.

Meanwhile, the head of an anti-bullying charity hit out at Gordon Brown after revealing several Downing Street staff have called its helpline.

Christine Pratt said she had “seen red” after ministers rallied round to deny claims in a new book that the Prime Minister had been warned over his treatment of staff.

Lord Mandelson said the Prime Minister was emotional, demanding and impatient but not a bully after a new book detailed a string of alleged outbursts.

But Mrs Pratt, who founded the National Bullying Helpline after being a workplace victim herself, accused them of failing staff by “going into denial”.

“I have personally taken a call from staff in the Prime Minister’s office, staff who believe they are working in a bullying culture and that it has caused them some stress.

“We would have hoped Gordon Brown would lead by example. If an employer receives complaints they should investigate,” she said.

“I am not saying Gordon Brown is a bully, I am not a judge. But I am appalled at the outright denial that is going on without due process being followed.”

Mrs Pratt said there had been “three or four” contacts with the helpline from Downing Street staff in recent years - although others were received before Mr Brown took charge.

The book, by Observer political commentator Andrew Rawnsley, details a string of alleged incidents of verbal and physical outbursts by Mr Brown.

Extracts published by the newspaper featured accounts of Mr Brown pulling a secretary from her chair, “roughly shoving” an aide and four-letter word-filled rants that frightened staff.

Mr Rawnsley said Cabinet Secretary Sir Gus O’Donnell was so concerned he delivered a “verbal warning” to the PM - a claim denied by the Cabinet Office.

“It is completely untrue to say that the Cabinet Secretary ever gave the PM a verbal warning about his behaviour,” a spokeswoman said.

But Mr Rawnsley said he was “100% sure”, based on first-hand evidence, that Sir Gus had looked into Mr Brown’s behaviour and personally warned him to calm down.