The growing popularity of Jeremy Corbyn in Labour's party leadership contest could cost Tessa Jowell the party's nomination for mayor of London, according to her rivals.
Polls have previously suggested that Tessa Jowell, perceived as being at the centre of the party, stands the best chance of beating probable Conservative candidate Zac Goldsmith in next May's election to replace Boris Johnson as mayor of London.
Members of rival Labour mayoral campaign teams have told BuzzFeed News that the influx of new registered supporters signing up to vote for Corbyn in the leadership contest could push out Jowell, who helped bring the Olympics to London and is closely associated with the Tony Blair era.
"The Corbyn effect seems to be real, based on what people are telling us on the phone," said one source in a rival campaign. "Someone voting for Corbyn is unlikely to vote Tessa Jowell for the mayoralty. Her whole campaign is about winning, but it's increasingly clear that membership [cares more about] values.
"It would be very unusual for people to vote Corbyn and Jowell. The one thing they know about Jowell is that she's a Blairite."
London Labour members and registered supporters who spend £3 to sign up will receive ballot papers for both the party leadership and London mayoral selection in just two weeks' time.
Corbyn's support is thought to be particularly strong in London, raising the prospect that individuals who signed up specifically to vote in the leadership contest could have a substantial effect on the concurrent mayoral contest, even if they've given it little thought.
A shadow cabinet source who backs Jowell said the influx of new Corbyn-supporting members "probably would help" rivals such as Sadiq Khan, David Lammy, and Diane Abbott. All three MPs signed Jeremy Corbyn's nomination papers to enable him to stand for the leader of the Labour party.
But a spokesperson for Jowell's team insisted that fears of Corbyn supporters hitting her chances were overblown: "We are fighting incredibly hard for every vote but this sounds like wishful thinking. Tessa's One London vision is winning over supporters of all the leadership candidates and from people across the city."
Labour's London mayoral candidate will be unveiled on the morning of Friday 11 September, with the party leader announced on the following day.
YouGov's Joe Twyman said that while "we're judging a hypothetical scenario at the given moment in time", the most recent data suggests Jowell is the only mayoral candidate who currently has a clear lead over the Conservatives in the eyes of the general London public.
Other candidates have increasingly attempted to attach their own campaigns to Corbyn's in attempt to benefit from his growing popularity. Deputy leadership contender Angela Eagle has written pieces urging others to "lay off Jeremy Corbyn".