THE UK’s voting system is “rigged against the workers” and leaves “large parts of the country to wither on the vine", election experts say.

According to a new report, Westminster’s first past the post (FPTP) system, where the party gaining the most seats irrespective of its share of the vote wins the election, means resources are targeted in affluent marginal constituencies that can swing the outcome of elections. It also warns that the Tories could remain in power even if Theresa May's party fails to poll more votes than Labour at the next election.

However, the Scottish Conservatives say Labour has previously won elections under FPTP and say that leader Jeremy Corbyn is the barrier to winning future elections.

The report is backed by the influential Electoral Reform Society, which supports a system of proportional representation (PR), where the votes polled by a party are mirrored in its parliamentary representation.

It says: "FPTP continually gives governments elected with a minority of the popular vote untrammelled legislative power – with the constant 'swings' from an unwarranted majority for one side going to the other side meaning any achievements can be rapidly 'unwound'.

"The Westminster model gives carte blanche to governments elected on a small proportion of the vote – meaning the Tories can rapidly rip away the gains of a progressive government.

"We see this with the tug-of-war/see-saw on workers’ rights. The see-saw of majoritarian government in Britain has allowed for sweeping legislation that has eroded trade union rights."

The report, which will be published this week, is supported by the ERS, but written by members of ‘Politics for the Many’ – a campaign aimed at forcing Labour to back PR.

Mike Kirby, Scottish secretary of Unison, is among the group's signatories. Other backers include Howard Beckett, assistant general secretary of the Unite union, and Mark Serwotka, general secretary of the PCS civil servants union.

High profile Corbynites such as Ian Hodson, president of the BFAWU bakers union, and Sam Tarry, political officer of the TSSA transport union, are also backers.

The report says that switching to a system of PR would push parties to the left by forcing them to make a pitch to the entire electorate, and that under the current system Labour would have to make at least double the gains at the last election if it was to win an overall majority.

However, a referendum on replacing FPTP with the Alternative Vote (AV) – a preferential voting system where voters ranks candidates, but which is not a form of PR – was decisively rejected by the UK public in 2011.

The Scottish Parliament already operates under a form of proportional representation, the additional member system, which combines FPTP and PR.

A Scottish Conservatives spokesman said: “This is the same voting system that Labour have won majorities under in the past.

“Their problem isn’t first past the post, it’s that voters know that under Jeremy Corbyn the Labour party is in a state of disarray.”