Politician more angry about seat (12)

I believe the answer is:

crossbencher

I'm a little stuck... Click here to teach me more about this clue!

'politician' is the definition.
(I know that crossbencher is a type of legislator)

'more angry about seat' is the wordplay.
'more angry' becomes 'crosser' (I can't justify this - if you can you should give a lot more credence to this answer).
'about' is an insertion indicator.
'seat' becomes 'bench' (bench is a kind of seat).
'crosser' going around 'bench' is 'CROSSBENCHER'.

Can you help me to learn more?

(Other definitions for crossbencher that I've seen before include "Independent member of Parliament" , "Independent MP" .)

I've seen this clue in The Telegraph.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.