RAIL unions have demanded that London Mayor Boris Johnson stop posturing about pay and negotiate seriously over his plan to impose night working on Tube drivers.

The call came as London Underground shut down yesterday after four unions walked out for the second time in a month as part of a long-running dispute over plans to launch a new all-night service next month.

The mayor has long refused to negotiate with unions directly but yesterday the RMT and TSSA said the time had come for him to meet them face-to-face in a bid to end the dispute.