The Labour Party was able to increase its vote share to about 40%, a level which has often historically been enough for Labour to form governments on its own.
But Labour was unable to form a government because the Conservatives also increased their vote share, albeit by a smaller amount:
This large Tory vote share enabled the Conservatives to prevent the assembly of a grand coalition of the left. Much of the turnover came from the collapsing UKIP vote, which fell more than 10 points from 2015 levels. But some of it came from the SNP, which dropped 1.7 points and 12 seats to the Tories. And some of it even came from the Lib-Dems, who lost 0.5 points and failed to win over many anti-Brexit Tory voters. Labour took care of business, but the junior partners came up short. What went wrong?