The 'Peep Show' writer and actor, who previously described Corbyn as "fucking awful" and bemoaned him being "marooned in the 1980s", told his 388,000 followers on Twitter that he had been spoken to "very horribly" by so-called 'Corbynistas', decrying his political interventions as unhelpful.
Webb's announcement came in an exchange with a former Labour spin doctor.
Hopi Sen originally tweeted Labour's in-fighting had meant it was "not the best of days politically" but a casual remark from Webb turned into a tirade, in which he revealed having cancelled his standing order to pay his annual fee for Labour Party membership.
@hopisen I don't do Spotify but I did get round to some overdue admin. Standing order cancelled. Maybe I'll vote for them. Maybe not.— Robert Webb (@arobertwebb) November 18, 2015
Sen tried to win Webb back, saying the news he had left the party "distresses me" and calling on him to stay, but it was no good.
@hopisen but half the members think I'm doing the opposite of helping. And tell me about it very horribly. Eventually you just go fuck this.— Robert Webb (@arobertwebb) November 18, 2015
The exchange ended with Webb saying the decision was a "personal choice" and that he admired those 'moderate' members of the party willing to fight. Webb said: "I've just had it."
Webb later clarified his remarks in a string of posts, saying he "didn't mean to make some big deal announcement", but had many reasons for quitting the party.
He highlighted the appointment of Seumas Milne, Corbyn's controversial new director of communications, as one of his main concerns.
Regarding the slight ooby-doo, didn't mean to make some big deal announcement, was just chatting, albeit loudly in public (1/4)— Robert Webb (@arobertwebb) November 19, 2015
Lots of reasons, none of them especially noble, eg giving the likes of Seumas Milne £11 a month makes me feel sick. (2/4)— Robert Webb (@arobertwebb) November 19, 2015
There's probably more to it than that & maybe I'll try to write about it next time I feel going 10 rounds with the Corbytrons (3/4)— Robert Webb (@arobertwebb) November 19, 2015
But heart not in it now, any of it. Obvs lots of decent people voted for JC; I think they made a mistake but wish them well. That's it (4/4)— Robert Webb (@arobertwebb) November 19, 2015
Webb has previously said Corbyn was "almost GM designed by [the] Tories to lose the next election".
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