THE case for radical reform of the Westminster voting system has become undeniable following the most unfair and disproportionate result in UK electoral history, according to a major new report.

The Electoral Reform Society (ERS) described a "democratic crisis" in its analysis of last month's General Election, estimating that almost three-quarters of votes, some 22 million, were effectively wasted and one in ten people voted for someone other than their favourite candidate.

The 2015 election saw David Cameron won a slim majority, 331 of 650 seats, with under 37 per cent of the vote. Meanwhile Ukip won just one MP despite being backed by 12.6 per cent of voters.

The ERS has also warned that the "archaic and divisive" First Past The Post (FPTP) system is artificially dividing the UK, after the SNP won 56 of 59 Scottish seats with 50 per cent of vote. Labour, the Tories and the Liberal Democrats won just one seat each, despite being backed by a combined 47 per cent of Scots who cast a ballot.

Polls conducted by YouGov on behalf of the ERS have helped the organisation predict how the result would have looked under an alternative system. Under its preferred option, Single Transferable Vote, voters are able to rank their preferences in multi-member constituencies.

The system, already used in local government elections in Scotland, would have seen the SNP win 34 seats north of the border, with Labour 14, the Tories eight and LibDems three. UK-wide, the Tories would have won 276 seats, 40 more than Labour, with Ukip picking up 54.

Under the list proportional representation system, used for second votes in Holyrood elections, the SNP would have won 30 Scottish seats, Labour 15, the Tories nine, LibDems four and Ukip one. UK-wide, Ukip would have won 80 seats and the Greens 20.

Despite doing well last month out of FPTP, SNP Westminster leader Angus Robertson said his party remained committed to pushing for a proportional representation system.

However, polling expert Professor John Curtice warned that following Mr Cameron's victory a change was likely to remain off the table for the next five years at least.

Katie Ghose, chief executive of the ERS, said that the report shows definitively that the current Westminster voting system is "bust".

She added: "That nearly three-quarters of votes were wasted this election shows that we have a democratic crisis on our hands, with most people's votes not counting.

"We have an archaic and divisive voting system that leaves millions disenfranchised and forces millions more to feel that they have to vote for a lesser evil - instead of who they really support.

"First Past the Post is artificially dividing the UK - giving the SNP nearly all Scottish seats on half the vote, while excluding Labour from the South of England and over-representing them in Wales and under-representing the Conservatives in the North of England and Scotland.

"At the same time, cross-community parties in Northern Ireland got a tenth of the vote and no seats, yet the DUP received nearly half the seats on just a quarter of the vote. Our voting system is breaking up Britain."

The ERS has argued that FPTP was designed for a two-party system that no longer reflects the reality of British politics. The recent campaign saw seven leaders take part in TV debates, with the number of votes cast for parties other than Labour, the Tories or LibDems rising to its highest ever level.

Professor Curtice, professor of politics at the University of Strathclyde, said FPTP was now failing deliver what even its advocates claimed was its main advantage in delivering substantial majorities to election winners.

He added: "Nothing is going to happen in the next five years. The problem is the party in opposition may dabble with changing the system, then when they win on the current system they decide they rather like it.

"It will probably take a hung parliament in the future before we revisit this substantially."

Mr Robertson, now the Westminster leader of the third largest party in the Commons, said: "The Westminster system is badly in need of reform. The SNP has done well under first past the post this time but we have always supported proportional representation and will continue to do so.

"From an unrepresentative voting system to the absurdity of the unelected House of Lords, SNP MPs will be a strong voice in the coming years for the change we need to see."