If the votes in the 2015 General Election had been measured differently – Ukip could have won 80 seats while the Greens could have ended up with 20 MPs, according to a new report.

A more proportional method of allocating seats on Thursday, May 7, would have meant Ukip and the Green Party’s combined five million votes would have translated into a lot more than the one seat they each won.

Why would the alternative voting system change the General Election outcome?

(Rui Vieira/PA)

Ballots are currently measured using a first-past-the-post system, which means it is the candidate who gets the most votes in a constituency wins that seat. Kinda like – winner takes all.

But the Electoral Reform Society (ERS) has analysed how the outcome would have been different with an alternative voting system, which would take into account all the votes from every constituency as a whole and then dish out seats accordingly.

How would the General Election outcome be different with an alternative system?

(Lynne Cameron/PA)

The ERS, which wants to introduce an alternative election system, worked out that if votes were measured by proportional representation similar to in the European elections, the Conservatives would have 89 less seats (242).

Labour would have won 208, which is 24 less, the SNP would have 26 less seats (so, 30), the Lib Dems would have 47 (+34), Plaid Cymru 5 (+2), Ukip 80 (+79) and the Greens 20 (+19).

What does the ERS have to say about it?

(Matt Dunham/AP)

Katie Ghose, chief executive of the ERS, said: “May 7 was the most disproportionate election in British history.

“It’s about time we had a fairer system for electing our MPs.

“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.

“The Greens and Ukip won 5m votes and just two seats between them. This is simply unsustainable – and can only end badly.”

What other General Election voting systems could there be?

(Kirsty Wigglesworth/AP)

ERS also commissioned YouGov to survey 40,000 people on how they would vote if they had to rank the political parties in order of preference – with the winner being the person who gets more than 50%.

This system would see a similar result to the Conservative majority we saw in May with Prime Minister David Cameron’s party being allocated six extra seats, Labour losing five, the SNP losing two, the Lib Dems gaining one, with no change for Plaid Cymru, Ukip or the Greens.

There could also be a single transferable vote system, similar to the one used in Scottish local elections. Under STV Ukip would have won 53 more seats and the Greens an extra two.

Who is opposed to an alternative voting system?

MP Dame Margaret Beckett (Fiona Hanson/PA)

The British public actually chose to reject a reform of the voting system in the 2011 referendum.

Labour MP Margaret Beckett, who chaired the No to AV campaign told BBC Radio 4′s Today programme that recent polling suggests voters want a system which delivers a majority government.

She added: “One of the virtues of our present system is that the British people understand it, they know how to work it.”