Part 4: 2017 - The biggest upset in UK political history

In the 2017 General Election, Corbyn had managed a record boost in the Labour vote share from 30.4% to 40.3% and added an impressive 3.5 million voters to Labour's vote total. The election resulted in a hung parliament. A few hundred votes in just a handful of marginal constituencies would have put Corbyn in Downing Street.

Data Source: Wikipedia

Blair increased Labour's vote share by 8.8% in 1997, but after just 21 months as Leader of the Opposition, Corbyn increased it by a massive 9.6%. This was the biggest increase in vote share in any election since 1945. Corbyn won just under 12.9 million votes, which was 2.1 million more votes than Blair in 2001 and 3.3 million more than Blair in 2005. As previously explained, population growth cannot be used to explain away this comparison, because prior to 2001, no party had been elected with less than 13 million votes since 1974; yet between 2001 and 2015, Labour's vote averaged around 9.6 million.

This was the first time Labour actually increased its number seats in an election since 1997. 2017 was the biggest upset in UK political history (a fact even acknowledged by the right-wing Daily Express), not least because opinion polls had consistently predicted a massive Tory landslide and Labour wipeout, with an expected Tory majority of between 100 and 200 seats. Theresa May was supposedly leading by 21 points at the start of the campaign. The inaccurate predictions persisted to the final week of the campaign when most polls still predicted a big Tory majority of up to 126.

In practice, Labour's extraordinary surge destroyed the Tories' majority. Theresa May was forced to do a £1 billion deal with the DUP to stay in power, but she was a lame duck Prime Minister and suffered defeat after defeat in the House of Commons. Knowing they could not pass legislation, the Tories cancelled their entire manifesto programme to focus on Brexit. However, they were blocked at every stage and forced to postpone the Brexit date twice, after which Theresa May was removed from office.

Labour's Brexit position seemed to work in its favour in 2017. Both the Tories and Labour neutralised the Brexit issue by agreeing to honour the referendum result. The UKIP vote collapsed from 12.6% in 2015 to just 1.8% in 2017.

Labour's result was all the more remarkable considering several factors:

• It was called less than 2 years into Corbyn's tenure as Labour leader and he inherited a severely divided and electorally weak party
• In the post-Referendum era, there was a new dividing line in UK politics over Brexit - a third of Labour voters had voted to leave the EU and now the Tories were offering to implement the policy which had gained a mandate of 17.4 million votes the previous year
• It was a snap election called at a point when the Conservatives were high in the opinion polls
• Conservative MPs had avoided a divisive leadership election in 2016 when Theresa May was elected unopposed
• Corbyn was characterised in the media as being extremely unpopular with voters
• His own parliamentary colleagues had launched a coup against him less than one year beforehand (and less than one year into his tenure), with his shadow cabinet resigning one by one in a coordinated attempt to shame him in the media and force him to step down
• 9 months before the election, he had faced a leadership challenge from Owen Smith, with Labour MPs overwhelmingly supporting Smith, then subsequently Smith and other MPs declined to help unify the party by refusing to return to the shadow cabinet
• The conventional wisdom is that divided parties are punished by the electorate - as exemplified by the scale of John Major’s defeat in 1997 

Apart from the persistent problem of rival opposition parties splitting the vote and an unhelpful distribution of Labour votes between constituencies, the main factor that stopped a landslide Corbyn win in 2017 was the fact that the Tories' vote also increased. The Tories also benefited from overwhelming media support and apparent bias in the coverage of her opponent. By harnessing nationalistic sentiment over Brexit and neutralising the UKIP vote, Theresa May managed to cling onto power, but she found herself unable to execute Brexit or carry through any major policies.

In Part 5 we'll look at why Corbyn was unable to turn the impressive momentum of 2017 into a general election victory in 2019.