How reliable are opinion polls when it comes to by-elections?

Two surveys suggest that the Conservatives will lose to Labour in both Uxbridge and Selby, writes John Rentoul

Keir Starmer’s Labour Party has the lead in a number of by-election polls (PA)

Several opinion polls have been carried out in constituencies where by-elections are under way or imminent, providing a snapshot of how the parties stand.

In Uxbridge and South Ruislip, where Boris Johnson stood down rather than risk being “recalled” by his constituents, Labour’s Danny Beales is eight percentage points ahead of the Conservative candidate, Steve Tuckwell.

In Selby and Ainsty in North Yorkshire, where Nigel Adams, Johnson’s ally, resigned after not getting a peerage, Labour’s Keir Mather is 12 points ahead of the Tories, who have yet to choose their candidate.