Decision made in the end. Taking the offer.
I think there are a few factors here to consider.
A 20K/yr paycut is significant.
Are you able to afford that much of a drop in income? It sounds like you’ll be investing a lot of energy into learning the skills for this job. You do not want to couple that with stress from increased financial strain.
This is dev experience.
Even if it doesn’t work out long term, it is still experience. If you work there at least 6 months, it can make your resume just a little more appealing for the next dev job you apply to.
How’s your relationship with your current employer?
If you’ve got a solid relationship with your boss, you could approach them and say “Hey, I know I’ve spoken to you about my goal to transition to a dev role. I took an interview for a position with another company, and it sounds like they are seriously considering me. But I love the team here and I value the work, and I’d much rather take on a dev role here. Is that something that could happen within the next 3 months?”.
I don’t recommend doing this if you don’t have that kind of professional relationship, though. It can completely backfire on you.
Also, while it’s good to be putting thought in to this now and considering your options - this isn’t a sure thing yet. You’ve got time to keep pondering. No need to rush into anything.
Sounds like it is time to put some serious thought into this. If you are thinking about taking the job offer, here’s another thing to consider: If this new position goes bottom up, are you on good enough terms with your current employer that you’d be able to rehire?
Congratulations! . £20,000 is a significant pay cut and you might not enjoy the work. It might be worth hanging onto your current position and discussing an internal transition/work experience if you are on good terms with your upline.
At least you have established that your current skillset is impressive enough to land you a dev job.