Voters in south London’s Tooting district will choose a new member of Parliament in a test of support for the ruling Conservative and opposition Labour parties just days before the U.K. decides whether to leave the European Union.

The probable date for the vote to replace Labour’s Sadiq Khan, who was elected London mayor last week, is June 9 or June 16, Labour Party managers said on Twitter on Tuesday. That’s either one or two weeks before the referendum on a so-called Brexit and will mean Tooting’s voters going to the polls three times in seven weeks.

Khan won the constituency in last year’s general election with a 47 percent share of the vote, but the Conservative candidate, Dan Watkins, won 42 percent in an improvement on the Tories’ 2010 performance.

It will be the first parliamentary by-election in southern England for Labour since Jeremy Corbyn became leader in September. While Khan gained a record vote in the mayoral contest, he distanced himself from Corbyn’s hard-line socialist policies during the campaign.

Labour lost ground in other elections around the U.K., particularly in Scotland. Corbyn told lawmakers on Monday that the party will need to perform better or it is on course to lose the 2020 general election.

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