Mick Lynch has admitted that public support for rail unions has been dented by weeks of strikes, but said the government was still “losing the argument” in the long-running pay dispute. The general secretary of the Rail, Maritime and Transport workers’ union (RMT) said that moves by Rishi Sunak to tighten anti-strike laws showed the government was hoping to close down opposition to austerity. Lynch made the comments on the picket line at Euston station in central London at the start of another 48-hour RMT walkout on Friday, the last stage of almost four weeks of varying levels of industrial action and disruption on the railway network. Only about 20% of train services were running on Friday, due to the strike – an improvement for most passengers in England, after a strike by drivers in the Aslef union on Thursday stopped virtually all trains at affected operators. The Department for Transport (DfT) said on Friday afternoon that train operators had sent a written offer of an 8% pay rise over two years to train drivers in the Aslef union – a 4% rise backdated for 2022 and a further 4% from January 2023. However, the proposal would oblige drivers to work on Sundays, among other changes to working practices. Steve Montgomery, the chair of the Rail Delivery Group, said it was a “fair and affordable offer in challenging times, providing a significant uplift in salary for train drivers while bringing in common-sense and long-overdue reforms”. The RDG said it would take the average train driver salary to almost £65,000. Aslef said it had yet to receive the offer. Earlier in the week, the union’s general secretary, Mick Whelan, told the Guardian that an offer demanding widespread workplace reform while not matching inflation would be rejected by members. Friday’s RMT strike, which included thousands of signallers at Network Rail as well as train crew, wiped out most services in Wales, Scotland and rural England, with no early morning or evening trains across Britain and only a limited schedule on main intercity and commuter lines. The strike will continue on Saturday with a similar level of trains available to passengers, who have been warned to undertake rail travel only if necessary. Most trains should be running by late morning on Sunday, although some operators have warned that it will take all weekend to restore normal services. Meanwhile, the RMT’s Mick Lynch told the PA Media news agency: “We’ve taken a little bit of a dent in public opinion.” But he said the support polled was “a very good score” given the strikes, adding: “We expect that to come back as people get over this latest phase. Our numbers are at record highs for an industrial action campaign. As they are for the nurses, and the teachers, and the posties, and everyone else.” The railway was “in desperate straits”, Lynch said: “The companies that run it and the government that oversees it have shown that they are incompetent and incapable of understanding the railway. “When we are not on strike, the passengers are told that due to shortages of staff trains aren’t running. At the same time, they say to me at the negotiating table that they want to make thousands redundant.” Legislation to block strikes showed the government was losing the argument, Lynch said. He told the BBC: “It is really important in a democratic society that we have free trade unions that represent working people. What this is a symbol of is that the government are losing the argument. “They’ve lost the argument on austerity and pay, and the state of our national public services. And instead they want to close that argument down by closing down the unions and stopping us from campaigning against poverty.” Sunak, in interviews on Friday, did not rule out the prospect of people being sacked for going on strike. The prime minister said he believed in the freedom to strike, but added: “I also believe that that should be balanced with the right of ordinary working people to go about their lives free from significant disruption.” Labour said that Conservatives, including the transport secretary, Mark Harper, had made clear that a policy of minimum service levels on the railway was not a solution, while the Department for Transport’s own internal impact assessment suggested it would increase strikes. The party also highlighted recent comments by the chief executive of the Rail Safety and Standards Board, Mark Phillips, who said any such legislation “won’t make the slightest bit of difference” to how many trains the industry could run. Union leaders will meet ministers on Monday. No further rail strikes are scheduled.