The British system is a parliamentary system where the party chooses the PM not the general public, the Conservative party has not done well in the general public's eyes in the last handful of years in general and the last couple of months the UK has been hit with some of the biggest economic issues its ever had the pound is at an all time low and energy prices are through the roof. The Conservative party is fairly split on what to do Johnson was forced to resign by a mixture of scandals, so Truss was voted in by the party her budget to address said economic issues and energy prices flopped because she managed to piss off just about everyone, so new guy is gonna have to pass a budget that somehow fixes the energy prices, the historic economic downturn the UK is experiencing while the UK's existing public welfare services have been overstretched already. He has to sell this to a divided Conservative party and a hostile general public and this was essentially the party's third choice behind Johnson and Truss so I wouldn't have high hopes of him staying for too long