Thousands of London Underground workers could be balloted for strikes in a series of rows over staffing and safety.

The Tube's two biggest trade unions said ticket office closures, lone working and the use of agency and security staff amounted to an "unacceptable" attack on safety standards.

The Rail Maritime and Transport Union and the Transport Salaried Staffs Association have told Tube bosses they will start balloting 7,500 drivers and station staff unless the disputes are resolved within the next few days.