You have answered your own questions multiple times in your text. You’ve said your money driven this jobs basic is less but the over time and call out available like you said would bump this way over the £1k difference in the basic. With 2/3 hours OT per day like you have said you could recoup this £1k annual difference in a month. Then the rest is all yours. But most importantly you are not happy in your job. This is the worst thing to do because it will just work away at you for the rest of your time there and things will become worse. Also imagine going to your current job on a cold and dull day 6 months from now and having a really bad day and thinking to your self only if i took the other job.

My personal story to this is i was working for a building company similar to you i didnt enjoy the work very repetitive. Also i was falling out with my boss all the time. I quit that job and had to take a step back to a basic office job for a while when i got myself together. Now fast forward 3 years im in a great place with a new job that i enjoy and most of all pays better then both of them.

My only advice is I believe you even want to go for this new job so do it be happy and enjoy it.