It's not credible to me to say that £43k is mid level. That's a junior salary for any tech position.
Regarding DevOps, it is so bad in demand right now, you'll get 60-70k easy without lifting a finger if you can handle any interview. There is noone to take these jobs anyway, all people who are interested in money have long gone contractors at > 500 £ a day anyway.
Everyone I've talked to about it is in a similar ballpark.
I expect ALL companies to pay better than what you have now: https://news.ycombinator.com/item?id=13541679
Do they ask how much you're currently paid and you reply 20k ? They will definitely use that information against you. You're so low that you might have to jump to 3X, then leave again in 6 months to go higher.
What's you linkedin? Link to you resume? What's your degree? Can you handle the usual 3 hours whiteboard marathon?
Lots of my grad friends fro ma top UK university were offered in their high 20's to start. But added bonuses. So one was 28k+2k bonus in first year. After 3 years, moved to 40k+bonuses.
Only have one friend who made 40k as a junior, he's one of the best coders i've ever come across. Oh and he went to work in finance.