The streaming thing is such an interesting one; I find the really big streamers very difficult to watch, it's always such over the top americanisms (Nick Mercs, TTT, Tfue, Dr Disrespect etc...). They rake it in because the American market is so huge & seemingly that's what they like.
For me, success in streaming is 90% how entertaining people find you, not how good you are at whatever you're playing. Out of that list you have to go down a fair way to find the people that are winning the tournaments - Ayden for example wins a lot of competitions but is a relatively dull/not engaging streamer (still earning a chunk though).
I think it would be very difficult for a UK based streamer to start now & gain enough of the market to earn enough to not have to have another job but still lead a normal life. There are a few that are probably making enough; Tommey (British but based in the US), Fifakill & Jukeyz (they're in the UK but have to play in the US overnight to earn a wage), BennyCentral (mostly works for Xbox but streams on Youtube too) but they've all been grinding for years.
Twitch is full of channels of people streaming all day & night to less than 100 people (most of whom won't be paying anything), when you'd probably want, I don't know, 1k subscribers per month maybe to pay for rent, food, clothes etc?
Really difficult but doable I suppose if you've got some entertaining USP.