BRITAIN’S biggest rail union warned today of “mass industrial action” after Reform UK’s London mayoral candidate raised the prospect of automating the city’s Tube network.

RMT made the threat after Laila Cunningham said the move would be a means of “undercutting” the power of trade unions as she was announced as the party’s candidate on Wednesday.

She pledged to automate every Tube train unless the unions and Transport for London (TfL) “start working for Londoners.”

A spokesperson for the Rail, Maritime and Transport union said: “Upgrading just three lines on London Underground would cost in the region of £20 billion.

“TfL does not believe it is economically viable and it would not be safe.

“Drivers on the Tube perform a skilled and an essential safety-critical role every day.

“Along with station staff, and other grades, they are vital in emergencies such as the 7/7 terrorist attacks where members of our union performed heroically, assisting emergency services in saving lives.

“Any attempt to move towards driverless trains in the future will be met with mass industrial action over a sustained period of time.”

A spokesperson for the drivers’ union Aslef said: “TfL staff are working hard for Londoners every day.”