Labour has suspended MP Chris Williamson over remarks about the party's handling of anti-Semitism.
The Derby North MP said Labour had "given too much ground" in the face of criticism over the issue, but later said he "deeply regrets" the remarks.
A number of Labour MPs had called for his suspension and the parliamentary party said he was no longer welcome at their meetings.
A Labour spokesman confirmed he has now been suspended "pending investigation".
Mr Williamson told the BBC that he was "absolutely determined" to clear his name, and that he did not want anyone to think he was "minimising the cancer of anti-Semitism".
The row erupted after footage was published by the Yorkshire Post, showing Mr Williamson, who is a close ally of Jeremy Corbyn, telling activists Labour had been "too apologetic" over anti-Semitism and was being "demonised as a racist, bigoted party".
It also came just a week after nine Labour MPs quit the party, citing anti-Semitism as one of the main reasons for the move.
WATCH: Chris Williamson tells a Sheffield Momentum meeting that Labour has been "too apologetic" about anti-Semitism... pic.twitter.com/zxtKdHQPvw— Liz Bates (@wizbates) February 26, 2019
At a meeting earlier on Wednesday, at which Mr Corbyn and the party's general secretary Jennie Formby were not present, the Parliamentary Labour Party (PLP) agreed the Mr Williamson should be suspended immediately.
Labour had put the MP under "formal notice of investigation" over a "pattern of behaviour" relating to the long-running row over anti-Semitism, but a decision was later taken by Ms Formby to suspend him.
Mr Williamson is reported to have held a meeting with aides of Mr Corbyn's shortly before Prime Minister's Questions began at midday.
Minutes later, he issued a statement on Twitter apologising, saying he never meant to downplay the "pernicious and cancerous" nature of anti-Semitism.
But senior figures called for Labour to go further and take disciplinary action, with ex-leader Ed Miliband describing the row as "a test" for the party.
A number of Labour MPs have taken to Twitter to welcome the decision by the party.
But Margaret Hodge questioned why it had taken so long to suspend Mr Williamson.
"He has form," she told the BBC. "He has done this before, he has apologised before and then he has done the same thing again.
"In the current climate not to show strong, immediate, determined action to stand out anti-Semitism was a mistake. The fact it has finally happened is a relief."
Wes Streeting also welcomed the suspension, adding: "We got there eventually and I hope that this sends a message to other people in the Labour Party that dismissing or delegitimising concerns about anti-Semitism isn't acceptable."
Strongly welcome the suspension of Chris Williamson. We got there eventually and I hope that this sends a message to other people in the Labour Party that dismissing or delegitimising concerns about antisemitism isn’t acceptable.— Wes Streeting MP (@wesstreeting) February 27, 2019
Mary Creagh said the suspension was "not a moment too soon", and Stephen Kinnock tweeted: "About time."
'Swift, but not swift enough'
Analysis by Iain Watson, BBC political correspondent
The suspension of Chris Williamson was relatively swift, but not swift enough to suggest there has been a sea-change in dealing with the problems of anti-Semitism in the party.
The initial briefing from sources close to the Labour leadership was that Chris Williamson needed to apologise, withdraw his comments and be subject to an investigation into "his pattern of behaviour".
If he had also been suspended at this stage, it would have been a clearer signal that the leadership were imposing their avowed policy of "zero tolerance" on the issue.
But it wasn't until Labour's deputy leader Tom Watson, its reviewer of anti-Semitism cases Lord Falconer, and some of the party's prominent Jewish MPs intervened that the suspension took place.
There seemed to be a greater willingness to do this in some parts of the party machine than others.
But with disagreements behind the scenes over the precise sanctions to deploy, Labour allowed their political opponents to steal a march at Prime Minister's Questions - and gave more publicity to The Independent Group, which has alleged the party is "institutionally anti-Semitic".
Labour has struggled to contain a long-running row over claims of anti-Semitism - hostility or prejudice directed against Jewish people - within its ranks. Nine MPs quit the party last week, criticising the leadership's handling of the issue.
But at a recent Momentum meeting in Sheffield, Mr Williamson said "I have got to say I think our party's response has been partly responsible for that because in my opinion… we have backed off far too much, we have given too much ground, we have been too apologetic."
Amid applause from the audience, he went on to say: "We've done more to address the scourge of anti-Semitism than any political party."
Who is Chris Williamson?
- The 62-year old is one of the most outspoken MPs on the left of the party
- A former bricklayer and social worker, he was a councillor before entering Parliament
- Led Derby Council twice in the 2000s, where he formed a coalition with the Tories
- Elected as MP for Derby North in 2010
- Lost the seat in 2015 but won it back two years later
- Has called on critics of Jeremy Corbyn to be de-selected
On Tuesday, Labour officials criticised Mr Williamson for booking a room in Parliament for a screening of a film about anti-Semitism and the activist Jackie Walker.
Ms Walker was suspended by Labour over allegedly anti-Semitic comments in 2016, and the documentary, Witch Hunt, looks at those and other allegations within the party.
Earlier this month, the Labour Party's general secretary, Jennie Formby, said the party had received 673 complaints in 10 months alleging acts of anti-Semitism by its members.