A drivers' strike disrupted one of London's busiest underground lines on Thursday as the drivers walked out, saying the trains were unsafe.

The walk-out on the Northern Line followed the failure on Wednesday of an emergency brake system designed to stop trains passing red signals.

Wednesday's failure was the fifth incident on the Northern Lineover the last month, unions said.

In the latest travel news, London Underground said the line, which carries 700,000 people every weekday, would remain closed on Thursday and Friday.

The underground company added it would not take any action against Northern Line drivers who were refusing to work on grounds of safety, a decision reportedly to be welcomed by the drivers' union.

The shutdown came a week after Mayor Ken Livingstone announced plans to boost London Underground fares by as much as a third.

Some of London's tube drivers had refused to work days after the second waves of attacks on London underground transport system after July 21.

They demanded London Underground to strengthen measures of safety, which among others include the return of guards to Tube trains, a return to dedicated gate-line staff that patrol ticket barriers, better equipment, such as breathing apparatus, for train operators and station staff.

(Shanghai Daily October 14, 2005)