Rail passengers are suffering more disruption on Friday because of a deadlocked dispute over jobs, pay and conditions.
Only 60% of trains are running, mainly because of a delay to the start of services after signallers and control room staff did not turn up for overnight shifts.
Some operators will wind down services slightly earlier than normal on Friday.
Members of the Rail, Maritime and Transport union (RMT) at Network Rail and 13 train operators went on strike on Tuesday and Thursday, with a third walkout planned for Saturday.
Members of the drivers’ union Aslef in Greater Anglia walked out on Thursday in a separate dispute over pay.
The Transport Salaried Staffs Association is balloting hundreds of its members at Network Rail and several train companies for strikes.
RMT general secretary Mick Lynch said: “Our members are leading the way in standing up for all working people trying to get a pay rise and some job security.
“In a modern economy, workers need to be properly rewarded for their work, enjoy good conditions and have the peace of mind that their job will not be taken away from them.
“Grant Shapps (Transport Secretary) needs to get in the room or get out of the way so we can negotiate with these companies who we have successfully struck dozens of deals with previously.
“What we cannot accept is thousands of railway workers being thrown on the scrapheap after being praised as heroes during Covid.
“RMT will continue its industrial campaign until a negotiated settlement is reached.”
Talks have been held throughout the week and will continue in the coming days, but there is little sign of a breakthrough.
Speaking on the BBC’s Question Time, Mr Lynch said: “The companies have told me face to face they could achieve a guarantee of no compulsory redundancies”, but added they “are not being allowed to”.
“They won’t write it down on a piece of paper and give it to us as a commitment,” he said, to which Conservative MP Rachel Maclean replied: “No organisation can give that guarantee.”
Prime Minister Boris Johnson branded the strikes a “terrible idea” and insisted there is “no point” having railways that are “so uneconomic” that ticket prices are prohibitive to passengers.
He also defended dealing public sector workers real-term pay cuts while giving pensioners rises in line with soaring inflation.
Speaking to reporters travelling with him in Rwanda, he said: “We’ve got to make the railways run economically for the very benefit of the railway workers themselves and their families.
“There’s no point having a railway system in this country that’s so uneconomic that you keep having to put ticket prices up and you have to drive more and more people off the railways.
“You can’t go on with practices like walking time with ticket offices that sell very few tickets. You need to modernise.”
The statutory instruments (SI) set to change the law to enable businesses to supply skilled agency workers to plug staffing gaps during industrial action will be laid on Friday and Monday, Downing Street has said.