Britain's specialist transport union has refused to rule out further industrial action as its latest strike cripples train services.
Members of the Rail, Maritime and Transport (RMT) union walked out on Saturday for the third time this week, with little sign of a breakthrough in discussions between the union and rail operators.
Only a fifth of services are running and half of the lines are closed. Passengers have been warned by rail operators that they should only travel by train if necessary and to check their journey in advance.
RMT general secretary Mick Lynch said the union's strikes could continue, given there is little sign of an end to the deadlock.
His comments came as he joined workers on a picket line outside Euston Station in central London on Saturday morning.
"We're not ruling out strikes but we have not put down any dates for any strike action," he told the PA news agency.
"We're going to review with our national executive next week, who have been all the way round the country this week on the picket line, so we're all going to get together the leadership of the union and see where we are.
"We are not going to name dates immediately and we're going to continue working constructively with the companies to strike a deal, but that is a really steep challenge at the moment because of the agenda they've got and the effects they want on our members.
Mr Lynch said they were hoping for "some compromise".
"Strike action's not ruled out and it will have to take place if we do not get a deal," he said.
"What we try to do is have the most effective strike action if it needs to take place. We're not just pretending.
"It's got to be a coherent and effective strike action because we don't want to waste our members' energy on something that doesn't work. We'll review that and see what we need to do if we need to take that action."
The union leader also had reproachful words for UK Transport Secretary Grant Shapps, who rejected as a "total lie" accusations by the RMT that he was wrecking negotiations by refusing to allow Network Rail to withdraw redundancy threats.
Mr Lynch hit back on Saturday, saying the union had not made any false claims.
"The railway last week was down by 80 per cent," he said.
"That has an effect that we don't particularly want to deploy and they are losing revenue commercially and that hurts them and it hurts our people because they've lost their wages. We don't want that.
"So if Grant Shapps wants to be constructive that's what he can do. He needs to tone down the rhetoric and get on with his job which is to settle this dispute."
Mr Lynch also hit out at the wider government, saying many ministers had never experienced the difficulty of manual labour.
"They're not using the system that they want and they've never worked in this type of work," he said.
"Many of them have never run a business, but they've also never worked on the tools. As my mother would say, they've never done a hand's turn.
"It's quite odd. The people who are running this country are brought up on a diet of Latin and Greek and our members are brought up on a diet of getting up at ungodly times to run the transport system. I think there's a bit of disconnect there.
"If we had people who were used to doing work, we might get a better deal out of them."
Boris Johnson calls for rail reform
The dispute comes after Prime Minister Boris Johnson said the public has a right to expect reforms to rail services.
"I would say, given the circumstances we're in, I think what we want to see is reform and improvement in the way the railways work, and modernisation," he told Sky News.
"When you've got a 25 per cent fall in ridership, which we've got at the moment, we've got the government putting billions and billions [into it].
"We're putting more into the railways than any previous government.
"I think the travelling public has a right to expect some basic reforms, like with ticket offices ... and some of these other practices that really nobody defends except the union leaders."