London's mayor has been accused of "engineering" a dispute over plans for all-night Tubes so he can blame unions if the new service is delayed.

Workers are set to strike again on August 5 in a row over pay and conditions for the night service, unless a breakthrough is made during talks which resume tomorrow.

Boris Johnson has been accused of "playing politics" to stop a settlement in the dispute.

TSSA leader Manuel Cortes said the mayor wants to blame unions for any delayed start to the service, due to be launched on September 12.

He said: "This dispute is being engineered by the mayor from City Hall. He has tied the hands of his negotiating team who are unable to make a new offer without his say so.

"By allowing next week's strike to go ahead, he will have an ideal excuse for delaying the start of the night Tube."

A spokesman for the mayor said: "The mayor believes that the offer that is on the table from London Underground is a very fair one and he urges meaningful dialogue on it to continue.

"He repeats his call for the unions to call off this unnecessary strike."