How Jeremy Corbyn could have been Prime Minister if Nigel Farage's 'voting reform' promise was in place ahead of Boris Johnson's 2019 Election win

Keir Starmer and Nigel Farage are both using the election campaign to push for a massive overhaul of the UK's voting system.

But analysis by MailOnline today lays bare how their demands of reducing the voting age to 16 and ditching the historic 'First Past the Post' arrangements could have changed the fate of Britain – by putting Jeremy Corbyn in No10.

The tendency of teenagers to vote Labour, together with the near-inevitability of coalitions under proportional representation (PR), would have prevented Boris Johnson from securing a landslide and 'Getting Brexit Done' in 2019.

Although the former PM would have led the largest party on 280 seats, only Jeremy Corbyn with 214 seats would have had a chance of cobbling together a 'rainbow' coalition to achieve a majority and install himself in Downing Street.

Projections using the popular D'Hondt method of PR — alongside demographic estimates and surveys of voting intentions — suggest the Lib Dems would have had 74 MPs. In reality, they achieved 11. 

Meanwhile, the Greens would have had 18 seats, compared to the one they actually won.

As a result, veteran left-winger Mr Corbyn, who supports unilateral disarmament and opposed Nato, could have been in charge through Covid and responding to the Russian invasion of Ukraine.

Critics of electoral reform say that ditching FPTP would simply lead to weak coalition governments, giving small and extreme parties disproportionate power. Many forms of PR would also lose the element of MPs representing specific geographical constituencies.

However, supporters of PR say the current system encourages tactical voting and is unfair. 

Mr Farage has pointed out that UKIP received six million votes in 2015, but only secured one MP. Although he has not spelled out exactly what arrangements he would prefer to FPTP, Mr Farage was an MEP for many years and many EU nations use the D'Hondt method of distributing seats for European Parliament elections.

Rishi Sunak this week accused Sir Keir of only wanting to lower the voting age because it was 'electorally helpful to him'. 

Speaking to the Daily Mail, the Prime Minister said of his rival: 'I think that tells you a lot about him and the Labour Party.'

Political commentators credit the FPTP system for helping the Conservatives stay in power for much of the past century.

If Sir Keir wins on July 4 and lowers the voting age, it would mark the largest change to the electoral roll since the last cut from 21 to 18 in 1969.

Speaking on a visit to Stafford earlier in the campaign, Sir Keir argued that young people 'should have a say on how their money is being used'.

Labour's manifesto – released last week – said: 'We will increase the engagement of young people in our vibrant democracy by giving 16 and 17-year-olds the right to vote in all elections.'

Teenagers aged 16 and 17 can already vote in Scottish and Welsh assembly elections,, the Isle of Man, Jersey, Guernsey, Brazil and Austria, as well as for some contests in Germany, Malta and Norway.

Opponents argue that teenagers should not be entrusted with the vote before they are adults, with the policy branded 'cynical' because it is only expected to benefit Labour.

Polls in the run-up to the 2019 showdown suggested 61 per cent of 16 and 17 year olds would have supported Mr Corbyn given the chance.

Only a fifth would have voted for Mr Johnson, according to a tracker by Survation.

On the night itself, Labour was the preferred option for all three cohorts under the age of 44 (18-24, 25-34 and 35-44). Tories were the party of choice for all the older groups.

Younger age groups usually see a lower turnout, however.

In the 2010 election between David Cameron, Gordon Brown and Nick Clegg, 18 to 21-year-olds had a turnout rate of 40 per cent – around half that of those aged over 65.

MailOnline's analysis was based on the voting intentions in a Survation poll of 16 and 17-year-olds in August 2019, which included just the options of: Tory, Labour, Lib Dem and Green.

Those results were projected on to the overall population in the age group, adjusted for the real turnout and then added to the total votes that were received by each party in 2019.

The D'Hondt method was then applied to the total votes to work out how many seats each would have gained.

Voting behaviour would almost certainly have been very different if Brits were operating under a PR system – but the findings do give a flavour of how different the outcome could have been under PR.

Some of Labour's biggest trade union backers – such as Unite and Unison – have also moved towards supporting proportional representation in recent years.

Labour hasn't officially backed a reform, although delegates overwhelmingly backed a motion calling on the party to embrace proportional representation at its annual conference in 2022. Sir Keir later stressed that it was 'not a priority', however.

Lucy Powell, shadow leader of the Commons, last autumn hinted that 'conversations' about ditching FPTP could take place if the party wins the general election.