The article with the maps & charts is suitable for B2 students and above, as it contains lots of visual information. The vocabulary is more suitable for B2+ students and above, who will encounter words like: a landslide [majority], a seat, to declare [a result], a tally, a gap, the share [of the vote], to plummet, to return [an MP], a constituency, the turnout. The article about the gap between votes and MPs is denser, and more suitable for C1 students, who will find interesting words like: a gap, share [of vote], to prompt, blatantly, flawed, first-past-the-post [electoral system], roughly [equal], a grandee, to boost, a hung parliament, to exact [a price].
If you want further info, you can read a short bio of each new member of the Cabinet in "Who is in Keir Starmer new cabinet?, a collection of notes which are suitable for C1 students. To find out more about the family background, professional and political career as well as the musical preferences of the new Prime Minister, you can listen to the Desert Island Discs programme on BBC Radio 4: "Sir Keir Starmer, leader of the oposition", which is a long recording (37:00) without transcript, first broadcast in 2020, which can be suitable for C2 students. You can also watch below his first solemn speech as a Prime Minister on this YouTube video with subtitles (C1 level):