A Second rail union is to join RMT in two 48-hour strikes in February to protest at plans to close all London Underground ticket offices.

Transport union TSSA said its members backed industrial action by 58.8 per cent and will now join the two walkouts from February 4 and 11 already announced by RMT.

The unions say the controversial plans to close all 260 Tube ticket offices will lead to the loss of 1,000 jobs and will affect passenger safety and security.

TSSA general secretary Manuel Cortes called on London Mayor Boris Johnson to end his "self-imposed boycott" of talking to rail union leaders.

"It is now time for Boris to sit down with his staff representatives and negotiate a sensible deal which will protect the safety and security of the travelling public as well as the long-term interests of our members.

"We think he is too ready to gamble with safety by abolishing permanent station supervisors in this closure plan, a plan which stands on its head his promise in 2008 to keep open every ticket office," he said.

RMT general secretary Bob Crow welcomed the news TSSA would join the strikes.

He said: "The TSSA ballot result steps up the pressure for a serious and renewed effort to resolve the issues that have forced our two unions into this dispute, which is simply about protecting safety, staffing levels, security and access to services for the growing number of Tube users."

Talks between London Underground management and the unions resume at conciliation service Acas tomorrow.