The leader of one of Labour’s flagship local councils, who resigned from his role last week, is being investigated by the party over an allegation of sexual harassment and unwanted touching, the Guardian understands. Lambeth council has rejected any link between the allegation and the announcement last week that Jack Hopkins was stepping aside after two years in the role. It is understood that Hopkins vehemently denies the harassment claims. In a message to fellow members of the Lambeth Labour group, Hopkins said he was quitting now “in order to give my successor the chance to deliver a unified group and platform in the run-up to the next election in 2022 so that we can continue to deliver for the people of Lambeth”. The council said in a statement that Hopkins believed that with the peak of the Covid pandemic seemingly over, it was time to hand over to a new leader. He plans to stay on as a councillor. Hopkins has also said his personal circumstances, including having moved home, also mean he is no longer able to remain council leader. However, the Guardian has been told that a woman made a complaint to Labour in March about sexual harassment by Hopkins. Hopkins self-referred himself to the party’s disciplinary system after the woman formally challenged him about his behaviour. Lambeth is a longtime stronghold for the party, and currently has 57 Labour councillors and only six representing opposition parties. Former leaders of the council include Steve Reed, now the shadow communities secretary. Marsha de Cordova, the shadow equalities secretary, is a former Lambeth councillor. Hopkins, who has been a councillor for 11 years, is a well-known figure within Labour local government circles, and appeared with Sadiq Khan during the London mayor’s re-election campaign. It is understood that the woman has been left disappointed by Labour’s process and that it came as a shock that, because Hopkins referred himself, her first contact with the process was when she was contacted by the party to say it had been told that she had potentially been a victim of harassment. She is believed to be concerned that Hopkins’s resignation could be a way to minimise the impact of an investigation, which would be heard by a sexual harassment disputes panel made up from members of the party’s national executive committee. A Labour spokesperson said: “The Labour party has a zero-tolerance approach to sexual harassment and we take all complaints extremely seriously.” The party is in the process of reviewing its complaints and sexual harassment procedures.