LONDON - Britain's Observer newspaper said Prime Minister Keir Starmer was expected to resign on Monday and set out a timetable for his departure, though a government source said Starmer remained focused on getting on with the job of governing.The threat to Starmer's position, which has been building for months, increased sharply on Friday when his rival Andy Burnham won a seat in parliament that would allow him to launch a formal leadership challenge.The Observer report said Starmer was discussing the ‌matter with his wife ⁠at his ⁠Chequers country residence before making a final decision, but that senior Labour figures expected a clear statement on his future as early as Monday.However, ​a government source said Starmer remained focused on his job and pointed to previous statements he has made to that effect.The ​British leader said on Friday he would fight any challenge to his leadership and urged Labour not to tear itself apart with infighting.STARMER'S POPULARITY HAS PLUMMETEDStarmer led the centre-left Labour party to a landslide election win in 2024 but ​has become deeply unpopular after a series of scandals and policy U-turns that ⁠have given ‌many voters an overall impression that he cannot deliver the improvement to their standards of ​living that he ​promised.If he were to quit or be ousted, it would mean the country installing its ⁠seventh prime minister in just over a decade - the highest turnover in nearly ​two centuries, reflective of anger at successive governments' failures to improve public services ​and tackle issues like illegal immigration.More than 100 elected lawmakers in Starmer's party - roughly a quarter of all Labour representatives in the House of Commons - have publicly said they want him to quit or set out a timetable for his exit, according to a Reuters tally.The Observer report, which did not name its sources, said Starmer had reached the conclusion that his position was no longer tenable after speaking to cabinet ministers, advisers, donors and trade union leaders.BURNHAM ‌WAITING IN THE WINGSBurnham, a 56-year-old career politician, is seen by many in Labour as the most likely successor to Starmer - whether through a negotiated transfer of power or a formal leadership ​contest.Having built a ​power base within Labour as ⁠mayor of Greater Manchester in northern England, he comfortably saw off the threat from Nigel Farage's right-wing populist party to win an election for a vacant parliamentary seat on Friday.Burnham did not immediately make a formal challenge to Starmer ​but used his victory address to promise a new path for the country. His allies have urged Starmer to agree to step down and hand over power voluntarily.Former health minister Wes Streeting has also said he is willing to challenge Starmer.The Times newspaper reported on Saturday that Burnham would sack finance minister Rachel Reeves if he were to become prime minister after his advisers concluded she did not represent a sufficient change of direction. Reuters could not immediately verify that report.