Ed Miliband
Former Labour leader Ed Miliband resigned from the top job after the general election Getty

A hitherto "secret" report into Labour's general election loss to the Conservatives at the general election has warned of "deep and powerful" negatives for the party. The analysis, which was commissioned by former interim Labour leader Harriet Harman and conducted in June 2015, only came to light after the publication of the party's own investigation into the May ballot.

The investigation was carried out by Deborah Mattinson and her Britainthinks polling firm. The leaked probe, based on 10 focus groups in Watford, Croydon, Nuneaton, Edinburgh and Glasgow, was published by ITV News less than a week after Margaret Beckett's investigation into the election.

Mattinson's report, among other things, described Labour's track record on the economy as "dismal". "It's become an incontrovertible truth: wasting money and spending money on the wrong things, money focused on people on benefits rather than hard-working families, bailing out bank with taxpayers' hard-earned money," the document read. "It's important to understand that the banking crisis is conflated with overspending. Voters describe the banking crisis as a 'curtain pulled back to reveal terrible truth.'"

Leaked Labour report
Section of the leaked reportITV News

The report was conducted before Jeremy Corbyn's shock Labour leadership victory, but provides some advice on how the party can rebuild its reputation and credibility with the British electorate.

Mattinson recommends Labour to "atone for its past", "show it takes Scotland seriously", "redefine and revitalise its brand" and "be for middle-class voters, not just down and outs".

Top Tory ‎Greg Hands, the chief secretary to the Treasury, said: "This secret report confirms that the public hasn't forgotten the mess Labour got us into with their borrowing, debt and taxes. Yet they are still in denial about their appalling track record on the economy and now Labour want even more borrowing, even more debt, and even more taxes. That's why the Labour Party remain a threat to Britain's economic security."

The embarrassing leak comes after Labour published its official review into the general election. Beckett claimed, among other things, that the party's policies were not too left-wing and that sections of the UK media attempted to "destroy" Miliband.

The document was publicly panned by Conservative election guru Lynton Crosby, who described the report as "arrogant". Labour had not responded to a request for comment from IBTimes UK at the time of publication.