THE UK’s "broken" voting system kept Theresa May in power and forced Scots to vote in the General Election based solely on the issue of independence, a landmark study claims.

May would have been defeated if the election had been held under the system of proportional representation that is used in Scotland rather than Westminster's First Past the Post, a new report from the Electoral Reform Society (ERS) says.

In a separate finding, the report highlights a surge in tactical voting on June 8 in Scotland based on either support for or opposition to independence. The ERS says it findings strengthen the case for scrapping the First Past the Post system (FPTP).

The ERS, which backs Proportional Representation (PR), sets out what it sees as the failing of the Westminster electoral system in the report called 'The 2017 General Election: Volatile Voting, Random Results'.

The report refers to how voters are "having to work around a broken two-party system" in UK general elections.

The report is based on a survey of over 13,000 adults across the UK in the aftermath of the election, that saw the Tories narrowly cling onto power despite losing their overall majority at Westminster thanks to a deal with the DUP.

However, ERS says that the Single Transferable Vote (STV) system, which allows voters to numerically rank candidates - one for first preference, two for second preference and so on - would have led to a Tory defeat, with Labour becoming the biggest party nationally.

Under STV, which is used in Scottish council elections and most Northern Ireland elections, many Green and Lib Dem supporters across the UK would have given their second preference votes to Labour to oust the Tories, the report says.

Labour would have attracted enough second preferences to make it the biggest party at Westminster, almost certainly forcing May from Downing Street.

The findings were based on a YouGov post-election poll of 13,273 adults that the ERS commissioned for the report, with people asked how they would have voted if they had been asked to rank the parties in order of preference.

Commenting on the survey results, the ERS report says: "Labour outperforms the Conservatives in our STV projection. This is largely because of stronger second and third preferences from the Liberal Democrats and Greens."

Willie Sullivan, ERS Scotland director, highlighted the claim that Labour would have been well placed to be the UK’s largest party if the election on June 8th had been held under STV rather than FPTP.

Sullivan, said: "Our projections show that had the General Election been conducted under the fairer system of proportional representation used for

Scottish council elections the result would have been different with Labour probably being the largest party."

Meanwhile the ERS said the fact that many Scots felt unable to vote for their party of choice because of the independence issue showed FPTP was flawed.

A key hallmark of the election in Scotland was the Tories winning 12 seats from the SNP after a campaign that party leader Ruth Davidson fought on the basis of opposition to a second independence referendum.

Sullivan, the ERS Scotland director, said the findings in the report showing that some voters cast their ballot solely on independence boosted the case for electoral reform.

He said: "Electors should be able to vote for parties they agree with on the broad sweep of policy, instead of feeling the need to vote tactically on the basis of one significant issue such as independence or Brexit because they fear ‘winner takes all’ dominance.

"A proportional system would allow for this and create a much broader discussion of politics to ensure all votes are of equal value with citizens feeling empowered to take part."

SNP MSP Alex Neil backed the ERS's call for PR for Westminster. However, Neil said the SNP lost seats because the party was squeezed by Labour performing better than expected and the Tories winning over more Unionist voters rather than the electoral system.

Neil said: "In multi-party Britain, the First Past the Post system is totally antiquated and there should be proportional representation for the House of Commons. But the reason people voted in the election was not determined by the voting system, but by the politics of the situation, which were working against us. We got squeezed from both ends with the Tories rocking the Unionist vote and Jeremy Corbyn's Labour proving more popular than expected."

Labour MSP Neil Findlay said the findings reflected the popularity of Corbyn, who is due to begin a five day tour of Scotland on Wednesday.

Findlay said: “This report confirms what we were hearing from people on the doorstep – that voters across the political spectrum liked what was being offered in the radical manifesto put forward by Jeremy Corbyn and the Labour Party."

Tory MSP Murdo Fraser said: “There are a number of advantages to First Past the Post, not least excluding minor fringe and extreme parties from obtaining parliamentary representation. We need to consider very carefully all the pros and cons of electoral systems before to abandon one that has served us well for many decades.”