Tony Blair's former spin doctor Alastair Campbell has been expelled from the Labour Party after admitting he voted for the Liberal Democrats in the European elections.
Campbell, a leading campaigner for a second referendum on Brexit, said he was "sad and disappointed" by the decision.
A Labour Party spokesman said "support for another political party or candidate is incompatible with Party membership".
Campbell, one of the key players in the New Labour era , insisted there was "plenty of precedent" of members voting for other parties or causes and pointed out Jeremy Corbyn's own rebellious past in Westminster votes during Blair's premiership.
And he said there was a difference in the swift way his situation had been dealt with compared to "the way anti-Semitism cases have been handled".
He said he would be appealing the decision to throw him out of the party.
In a series of posts on Twitter, Campbell said the email informing him of his expulsion came as the Labour leadership "finally seems to be moving to the right place on Brexit, not least thanks to tactical voting by party members, including MPs, councillors and peers" who back a so-called People's Vote.
"I was not intending to publicise this at this stage, but have had calls from friends in the Party telling me it is now widely known and likely to be leaked.
"I have been advised by lawyers with expertise in this field I have grounds for appeal against expulsion and shall do so.
"I am and always will be Labour. I voted Lib Dem, without advance publicity, to try to persuade Labour to do right thing for country/party."
He added the "approach also contrasts with our era" when Mr Blair was pressed to withdraw the whip from Corbyn for "persistently voting against Labour in Parliament" but said no.
Labour rules state that members who support a party other than Labour are automatically ineligible for membership.
Before Campbell's expulsion, former prime minister Blair said he understood why his ex-aide had voted Lib Dem.
Blair said he had voted Labour "without any great enthusiasm" at last week's European election.
Asked on Sky News what he would say tor Campbell, Blair said: "I understand why you did what you did. You wouldn't be the only person I know who has voted Labour all their lives who didn't vote Labour in this election."
