But Alastair Campbell, the party's former all-powerful communications chief, had his membership rescinded today after publicly admitting that he had voted for the Liberal Democrats at last week's European Parliament elections.
The 62-year-old, a vocal campaigner for a second referendum on Brexit, said he was left "sad and disappointed" by the decision and planned to appeal.
He claimed that he had voted Lib Dem to try and persuade Labour "to do the right thing", but "always will be Labour".
In a series of tweets, Campbell said: "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 antisemitism cases have been handled."
Campbell, who worked as a political journalist before becoming a key member of Tony Blair's staff in 1994, added that there were plenty of previous cases where members had voted for other parties and causes, and some were now senior party staff members.
Meanwhile, Labour leader Jeremy Corbyn said today that his priority remains a general election, despite calls to change direction after the party suffered a mauling from voters in the European elections.
Sir Keir Starmer, shadow Brexit secretary, has said a second referendum is the "only way" to break the Brexit impasse.
In his first comments since the election result, Mr Corbyn told the BBC his priority has not changed.
He said: "The priority at the moment, I think, is for this Government to call for a general election and actually have a general election so we can decide the future.
"There's no majority in Parliament, there's no legislative programme and Parliament has basically been given nothing to do by the Government.
"I think that is a demand that should be made and made as strongly as possible."
Mr Corbyn did not rule out another referendum, saying any Brexit deal should be put back to the people and that the UK should not be allowed to "crash out" with no deal.
He said: "John (McDonnell) has also pointed out, and I support this, that any final deal has to be put to a public vote.