Labour has been “completely taken over by a Leftist clique”, one of the party’s most famous supporters has said, after the woman in charge of handling complaints was ousted and replaced by a controversial Jeremy Corbyn loyalist.

Ann Black, the long-standing chairman of the Disputes Sub-Committee of Labour’s ruling National Executive Committee (NEC), was replaced by Christine Shawcroft, a director of the Corbyn-backing group Momentum, in a move that one party member said showed “contempt” for party democracy.

It came just a day after three Momentum supporters, including the group’s founder Jon Lansman, won places on the NEC to strengthen Mr Corbyn’s grip on the party.

Ms Shawcroft, who was suspended from the Labour party in 2015 for supporting the the Tower Hamlets mayor Lutfur Rahman, who was found guilty of electoral fraud and bribery, now controls the body that decides whether the party should investigate racist, homophobic, anti-Semitic and other bullying and abuse by party members.

The actor Sir Tony Robinson, best known for playing Baldrick in Blackadder, accused supporters of Mr Corbyn of “undermining” Ms Black, 66, who was awarded an OBE for political service in 2013.