Ministers and health unions are on the verge of a breakthrough in talks to resolve their long-running pay dispute that has triggered a series of NHS strikes in England, with an announcement expected on Thursday, the Guardian has been told. Sources said positive progress had been made on discussions about the awards for ambulance workers and nurses for both 2022-23 and 2023-24, although uncertainty remained about whether union members would accept the terms when they are balloted. After a week of negotiations, talks went on late into the night on Tuesday and looked likely to do so again on Wednesday, insiders said. The health secretary, Steve Barclay, was said to have been present “a lot”, with large sections of his diary dedicated to resolving the row. The Department of Health and Social Care (DHSC) emphasised the process was “ongoing” and refused to give a running commentary. But several insiders indicated they were confident an agreement was close. Two government sources indicated an announcement could be made as soon as Thursday. Another well-placed source put the chances of Barclay making a formal offer soon at “more than 50/50; about 60/40”. But the source added: “It’ll be an offer, not a deal. The unions still have to sell it, whatever it is, to their members, who may or may not accept it.” Several others with knowledge of the talks said they believed a breakthrough was imminent, but cautioned there had been “a few false dawns” before. It is three months since the first strike by the Royal College of Nursing (RCN), which is one of six unions around the table. The RCN was initially invited for talks with the DHSC three weeks ago, with other unions said to have been “quite cross” they were at first excluded. They then joined the process. All unions agreed to pause strikes to allow talks to proceed – a pre-condition set by the government. But Unison has not yet decided whether to go ahead with a strike next week. It has said that “whether or not planned strike action on 20 March goes ahead will depend on how talks progress”. However, the Guardian understands that while good progress has been made, especially with regard to Barclay offering extra money for 2022-23 – his £1,400-a-head award for NHS started the dispute – the size of the increase for 2023-24 is still a sticking point. One of those close to the negotiations said: “It does seem that the government are inching towards an offer; that they are close to making a formal offer.” They said it seemed “to involve a reasonably substantial one-off, non-consolidated payment for this year” to supplement the £1,400 across-the-board rise Barclay announced last summer. But they added: “It looks like the government is sticking to 5% being their best offer for next year; that they’re not budging on that. And that’s become problematic; that’s the problematic side of it. The government not offering any number above 5% is making things quite difficult, I understand. “Jeremy Hunt may have said in his budget that inflation will fall to 2.9% by the end of the year. But the RPI inflation rate in January was 13.4%, yet you’re going to ask union members to accept 5%? So I don’t know if people will buy 5%.” A DHSC spokesperson said: “The government, NHS employers and unions representing the NHS agenda for change workforce have been holding constructive and meaningful discussions covering pay and non-pay matters. These talks are ongoing.”