LONDON — The widower of the British lawmaker Jo Cox, who was killed in 2016 by a right-wing extremist, has stepped down from two charities created in her memory after accusations of sexual misconduct resurfaced in the British news media.

Brendan Cox, who had sought to continue his wife’s advocacy work and had spoken out about the rise of hate in Britain, said on Twitter that he resigned from the organizations More in Common and the Jo Cox Foundation this past week.

He was accused of inappropriate behavior in 2015 by a woman who worked with him at the charity Save the Children, and of assaulting another woman at Harvard University that same year, according to British news reports.

The reports first resurfaced this weekend in the tabloid The Mail on Sunday. The article includes part of a Cambridge, Mass., police report showing that the woman in the Harvard episode, whose name has been redacted, had accused Mr. Cox of “indecent assault and battery.”