Prime Minister Boris Johnson and his governing Conservative Party won a convincing victory in last week’s U.K. general election. The Conservatives captured 365 seats, sufficient for a solid majority in Parliament and fully 48 more than the 317 seats they won in the 2017 general election. Their main rival, Labour, fared poorly. Recording its worst performance in decades, Labour was reduced to 203 seats, down from 262 in 2017. What accounts for the election outcome?

Two major arguments have been offered why the Conservatives did so well and Labour, so poorly. The first is that the election was “all about Brexit.” Campaigning on the slogan “Get Brexit Done,” the Conservatives attracted a vast majority of people who supported leaving the E.U. Labour’s Brexit policy was ambiguous; Labour said that if it formed a government, it would negotiate a new deal with the E.U. and then hold a referendum to let the people decide — but in doing so would neither endorse remaining in or leaving the E.U. This uncertainty about where Labour stood, while Liberal Democrats and other parties forcefully advocated staying in the E.U., split the Remain vote. Since the overall division of opinion between Leave and Remain was very close, this gave the Conservatives a decided advantage.

The second argument is that Labour Leader Jeremy Corbyn is responsible for Labour’s debacle. Not only was his stance on Brexit confusing, his image was badly tarnished. Although Corbyn had been quite well received — especially among younger voters — during the 2017 election campaign, his poll ratings had fallen precipitously since, as he was accused of harboring anti-Semites in his party and being sympathetic to terrorist groups such as the IRA and Hamas. His opponents portrayed him as a left-wing extremist who would wreck the U.K. economy and threaten national security. In contrast, although Conservative Leader Boris Johnson was not wildly popular, his image was considerably more positive than Corbyn’s. Voters rely heavily on leader images when deciding how to cast their ballots. As a result, the idea that voters’ very negative reaction to Corbyn was pivotal for the election outcome seems sensible.

The authors of this article gathered data in a representative national pre-election survey of 2515 eligible British voters conducted by Deltapoll in the week before the balloting. These data enable us to assess the merits of Brexit versus Corbyn arguments, although it is always hard to know what causes what in public opinion data. As expected, Brexit was frequently mentioned as the most important issue in casting a ballot, by 59 percent of respondents. Forty-one percent said the Conservatives were the best party on the issue, and only 18 percent preferred Labour. Similarly, two-thirds of those reporting they would vote to leave the E.U. intended to vote Conservative in the general election. Among those saying they would vote to remain in the E.U. if they had that option, slightly less than half intended to vote Labour.

The survey also shows large differences in leader images. Johnson’s score on a 0 (dislike) to 10 (like) scale is 4.5, substantially higher than Corbyn’s, whose 3.6 rating is lower than any other leader’s score. Corbyn also fares poorly on leadership traits. Thus, 40 percent judged Johnson as competent, as compared to 27 percent for Corbyn. Similarly, 45 percent thought Johnson was a strong leader, but only 25 percent said this about Corbyn. Asked who would be the best prime minister, 36 percent chose Johnson and only 21 percent, Corbyn.

Leader images are strongly related with voting intentions. Among those scoring Johnson less than 4 on the 0-10 dislike-like scale, only 4 percent intended to vote Conservative. This climbs sharply to 40 percent among those scoring Johnson 4-6 on the scale and to fully 78 percent among those scoring him 7-10. The pattern of Conservative voting and feelings about Corbyn is reversed — nearly two-thirds of those giving Corbyn a low score (less than 4) on the dislike-like scale intended to vote Conservative as compared to only less than one in ten who gave him a high score (7 or more).

The graph shows how attitudes toward Brexit and feelings about Jeremy Corbyn are related to voting intention. Among people with scores less than 4 on the like-dislike scale (55 percent of all voters), the percentage intending to support the Conservatives climbs sharply from 35 percent among those favoring remaining in the E.U. to 83 percent among those preferring to leave. Similar patterns can be seen for those who are more favorably disposed toward the Labour leader, but attitudes toward Brexit matter less for these individuals. For example, among those giving Corbyn scores of 7 or greater (22 percent of all voters), only small minorities say they will vote Conservative (3 percent of Remainers, 17 percent of Leavers).

More comprehensive statistical analyses that consider a variety of other factors (long-term partisan loyalties, age, social class and other demographics) point to the same conclusion: attitudes toward Brexit and party leader images were both important for voting. However, the relationship with leader images was stronger.

Neither the “Brexit” or the “Corbyn” narratives about what drove the vote in the 2019 U.K. general election tell the whole story. Brexit was the leading issue; attitudes about it shaped much of the campaign debate and were strongly correlated with the choices voters made. But as is typical of U.K. elections, leader images also were powerfully related to voting. Although many people harbored doubts about Conservative leader Boris Johnson, his image was considerably more positive than that of his Labour rival, Jeremy Corbyn.

Queen Elizabeth II formally reopened Parliament on Dec. 19, setting out the government's legislative agenda with Brexit and healthcare as top priorities. (Reuters)

In the end, the Conservatives’ ability to position themselves as the only viable option for voters wanting to leave the E.U. combined with widespread reservations about Corbyn’s character and competence enabled the Conservatives to win big and send Labour a crushing defeat.

Harold Clarke is the Ashbel Smith professor in the School of Economic, Political and Policy Sciences at the University of Texas at Dallas and co-author with Matthew Goodwin and Paul Whiteley of Brexit – Why Britain Voted to Leave the European Union (Cambridge University Press, 2017).

Matthew Goodwin (@GoodwinMJ) is a professor in the department of politics and international relations at the University of Kent.

Marianne Stewart is a professor in the School of Economic, Political and Policy Sciences at the University of Texas at Dallas.

Paul Whiteley is a professor in the department of government at the University of Essex.