Labour MP Lloyd Russell-Moyle has been suspended from his party after a "serious complaint" was made against him.
The representative for Brighton Kemptown had been planning to fight for his seat again in the upcoming general election.
But Mr Russell-Moyle said there was not "enough time to defend myself as these processes within the party take too long".
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The nature of the complaint is not yet clear, but Sky News understands it was made last week, and an investigation is now pending.
In a social media statement, Mr Russell-Moyle said he believed it to be a "vexatious and politically motivated complaint about my behaviour eight years ago".
He claimed it was a "false allegation that I dispute totally and I believe it was designed to disrupt the election".
He added: "I will aim to cooperate with the investigations process to clear my name, but will now take this opportunity to contribute to public life in different ways under what I hope is a Labour government."
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Tap hereMr Russell-Moyle has been an MP for his Brighton seat since 2017, serving as a shadow foreign minister under Jeremy Corbyn and as a shadow environment minister in Sir Keir Starmer's first cabinet.
Before parliament shut its doors for the election campaign, he also sat on both the Commons' Net Zero and the public administration committees.
But he gained recognition from many across the House after revealing to his fellow MPs in a speech that he was HIV positive in 2018.
Another memorable moment saw him seize the mace in the Commons in protest over the government's handling of Brexit votes.
A spokesperson for Labour said: "The Labour Party takes all complaints extremely seriously and they are fully investigated in line with our rules and procedures, and any appropriate disciplinary action is taken."
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