Tom Watson is alleged to have been behind the account, which had almost 50,000 followers and had become increasingly prominent in recent weeks as RNLI staff faced harassment and attacks online. Far-right activists have targeted the charity over its crews' involvement in rescuing people trying to cross the Channel in small boats.
The account, which has a history of racist comments, appears to have used AI to scrape data from LinkedIn and other sites to build a so-called "Traitorbase". It was removed almost immediately after Hope Not Hate made its allegation and after the Guardian approached Watson for comment.
The account frequently praised the hard-right MP Rupert Lowe and claimed to have donated £2,500 to his Restore Britain party and joined its "Cromwell Club" for activists who pay a certain level of donation.
Chantelle Lunt, a Green party councillor in Merseyside who has already been targeted by the far right, made a report to police after details about her were published by the account. "Someone told me that I had been doxxed and when I went to look I saw that details about me appeared to be on a spreadsheet which included reference to other people who were involved in Stand Up to Racism," she said. "The climate at the moment is horrendous and I'm no stranger to people targeting me and my family, but there's a big concern when this information is actively put out there. You can see people engaging with it and actively encouraging each other."
A spokesperson for a targeted charity said: "This is another example of a cynical attempt to spread misinformation that has unfortunately gone unchecked on social media platforms. This is an attempt to sow discord and division among communities and prevent organisations trying to help the most vulnerable communities in this country from operating at their full potential."
The account also posted the photographs and names of business executives said to have been involved in hiring minority ethnic staff. One businessperson who was targeted described the doxxing as "bizarre". Last month the RNLI warned supporters their personal information may have been hacked.