London Tube drivers are to stage two 24-hour strikes on 6 and 7 December, the Rail Maritime and Transport (RMT) union has announced.

RMT said the action was the result of a “wholesale breakdown” in industrial relations, as well as breaches of procedures and bullying of staff.

The strikes are backed by drivers on the Piccadilly and Hammersmith & City lines.

The walkouts will coincide with strikes by Southern Rail guards in a continuing dispute over train door safety and the role of conductors.

Both walkouts will run between 9.30pm on Tuesday 6 December and 9.29pm on Wednesday 7 December, RMT said.

About 400 drivers on the Piccadilly Line are due to strike. The line is London’s fourth busiest and is the only Tube service with terminals at Heathrow airport.

RMT general secretary Mick Cash said: “The dispute on the Hammersmith & City line is about the basic issues of protecting working conditions of our members and defending agreements from attempts to drive a coach and horses through them.

“The management are out of control and the anger at their failure to follow procedures has boiled over.”

He added: “This breakdown in industrial relations should never have been allowed to happen and, if agreements and processes had been adhered to from the off, the package of issues at the heart of the dispute could have been resolved through the joint machinery.

“In the separate dispute involving drivers on the Piccadilly line, safety is again a major factor and is tied in with the ripping-up of policies and procedures and ignoring warnings from staff.”

“Our members have been left exposed and vulnerable and we have no choice but to blow the whistle before lasting damage is done.”