I think the pm changing is a new government in the legal sense or whatever since they have to go to the head of state saying they have the confidence of Parliament to form a government. There has only been 3 governments since 2019. The past 10 years have been a bit chaotic in UK standards. 2004-2014 had three different prime ministers with like 2 or more elections (I don't remember when the second Labour one was)
