As reports from picket lines indicated that London Underground was able to run only an emergency service between Elephant and Castle and Queen's Park, the union renewed its call for the company to take safety concerns seriously and negotiate. The 24-hour walk-out began on Thursday night.

The dispute centres on London Underground's attempt to impose lone-working at Queen's Park, Willesden Junction and Harrow and Wealdstone stations, increasing the risk of assault for station staff and drivers.

"Our members have today demonstrated how angry they are that LUL is still set on plans that will increase the danger of assault on our members at stations where trains are tipped out," RMT general secretary Bob Crow said from the Elephant and Castle picket line.

"This is a simple dispute about the safety of our members, and the 95 per cent vote for strike action should have told the company everything they need to know about their plan. We need London Underground to talk to us seriously, but they also need to listen."

The stations involved are in areas that have more than their fair share of violent crime problems, and it is hardly unreasonable to expect that there are two station staff on duty to give more security to each other and the public.

"It is our members who are out there trying to deliver a service in demanding circumstances, and their employer shouldn't be attempting to impose changes that make that job harder and more dangerous," Bob Crow said.