Talks were set to resume on Monday between the RMT and rail bosses, with the union’s national executive committee mulling further strike dates as the prime minister backed plans to close ticket offices. Services started returning to normal after a later start on Sunday due to the last of three 24-hour national strikes by workers at Network Rail and 13 train operating companies on Saturday. More walkouts could be called for late July. An RMT spokesperson said the union would “evaluate and look to the next phase of the campaign”. Speaking ahead of the G7 summit in Germany, Boris Johnson said that to justify the money spent on the railways, including the £96bn spent on the rail investment plan, “the travelling public and the taxpayer are going to want to see reform and improvement in the way the railways run” and there could not be “business as usual”. He told ITV News: “I can’t responsibly tell them that we’re just going to continue with business as usual, with the same old systems of ticket offices that are barely used, or sell one ticket every hour.” The Department for Transport has rejected TUC claims that the government had misled the public over its role in the dispute. Legal opinion obtained by the TUC from QC Michael Ford said that the transport secretary has “very extensive powers” over what can be agreed between rail operators and unions, and “very significant contractual power” to direct how disputes are handled. In Ford’s legal opinion, the contractual provisions binding train companies mean they “do not have freedom to negotiate the matters which have given rise to the current dispute”. TUC general secretary, Frances O’Grady, said: “We always believed that Conservative ministers had the power to pull the train companies’ strings, behind the scenes. And this legal opinion on rail contracts confirms it.” A DfT spokesperson said that it did not mean Grant Shapps should get involved in negotiations, adding: “He’s required to set the limits of taxpayer support and ultimately sign off on any deal – not to be involved in negotiating one – and his contracts with operators allow him to do precisely that.” Johnson’s intervention is likely to inflame tensions between rail unions, employers and the Department of Transport following the refusal to rule out compulsory redundancies that result from a planned modernisation of rail services, including the closure of ticket offices. Drawing on his role as London mayor, when he battled to close ticket offices in underground stations, Johnson added the government is doing “quite unbelievable things” on the railways, pointing to Crossrail and the integrated rail programme. “To justify paying that money, making those commitments. I think the travelling public and the taxpayer are going to want to see reform and improvement in the way the railways run,” he said. The shadow foreign secretary, David Lammy, criticised the government for not negotiating – but he also stated he categorically did not support airline workers who have also voted to strike over wage demands. Regarding the rail dispute, Lammy told the BBC: “This government isn’t negotiating. This government is not supporting reaching a compromise.” However, asked if he backed the claims of British Airways check-in and ground staff at Heathrow who have voted to strike to have a 10% pay cut restored, Lammy answered: “No, I don’t. It’s a no. It’s a categorical no.” He criticised Labour MPs who had joined picket lines. One, Nadia Whittome, announced on Saturday she would be donating part of her wage to the RMT’s local strike fund. The first results from strike ballots at another rail union, the TSSA, are due later this week, potentially escalating the dispute and the effects of any coordinated action. TSSA members include controllers and the managers who have been acting as contingency and back-up staff during the RMT walkouts. The union initiated its first ballots at train companies serving Birmingham, the host city of next month’s Commonwealth Games, as well as at Network Rail. Drivers at the Aslef union will, meanwhile, go on strike over pay on Tuesday and Wednesday on Croydon’s trams and next Saturday at Greater Anglia.