A member of the Labour disciplinary committee that failed to expel Ken Livingstone over his comments about Hitler and Zionism has criticised his colleagues for letting the former London mayor off the hook.

Peter Mason, an Ealing councillor and national secretary of the Jewish Labour Movement, is a member of the 11-person National Constitutional Committee but not one of the three who decided Livingstone’s fate.

He wrote on the website Labour List: “Reports in the press this week that some NCC panel members went into his hearing with their minds already made up to save him are deeply troubling and risk undermining the integrity of the process, the committee and the party. The allegation continues that in deciding on his punishment, the vital principle of proportionality under which the NCC operates was abandoned.

“Livingstone was found to have brought the party into disrepute on all counts. Expulsion would have been on the table as an option. A slap on the wrist is in not a proportionate punishment.”

Labour List speculates that Mason is referring to Russell Cartwright, who is a member of Campaign for Labour Party Democracy. He was joined by Brenda Warrington, a Tameside councillor, and Rose Burley, a Walsall councillor, on the panel.

It is believed Burley pushed for Livingstone to be kicked out while Warrington wanted to limit the punishment to suspension.