Tony Blair's former spin doctor Alastair Campbell has been thrown out of the Labour Party.
The People's Vote campaigner announced on Twitter that he had received an email informing him of the expulsion
The move comes after Mr Campbell admitted he had voted for the Liberal Democrats in the European elections.
A Labour Party spokesman said "support for another political party or candidate is incompatible with Party membership".
And during an appearance on the talkRADIO breakfast show yesterday, Mr Campbell said he would "consider" voting for the Liberal Democrats again in a general election.
However, Mr Campbell, a leading campaigner for a second referendum on Brexit, said he was "sad and disappointed" by the Labour Party's decision to expel him.
He added that 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 Mr Blair's premiership.
Mr Campbell posted a Twitter thread about his expulsion
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".
"Sad and disappointed to receive email expelling me from @uklabour - particularly on a day 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 @peoplesvote_uk," he wrote on Twitter.
"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."
He continued: "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. In light of appeal, I won't be doing media on this. But hard not to point out difference in the way anti-Semitism cases have been handled."