Cash also slammed Johnson for "refusing to get his hands dirty himself by talking to us".
Steve Griffiths, London Underground’s chief operating officer, said: “We have made a very fair offer on pay and the introduction of the Night Tube and 500 extra staff have been recruited to help run it. As we have shown already, we are prepared to be flexible to reshape the offer to best suit our staff.
"One of the points that we were able to clarify immediately today was that the Night Tube rosters were never going to be ‘imposed’ but had been made available to help staff see that we are serious about honouring our commitments on work-life balance. We will continue to make ourselves available at Acas for further discussions and trust that the trade unions will too.”