This sounds like a sensible philosophy...especially for me on career shift/life catch-up!
You should stick to your current job field until you have more knowledge and experience in IT, or programming, so you can afford to pay the bills while you are learning how to become a programmer. Don't make the mistake of trying to switch careers too early and put yourself in a financial bind that makes everything harder to accomplish.
I understand the education system in the UK is very different (and frankly so much better) than here in the USA, but for the most part, having a job that pays well is still important while you are preparing yourself for a career change.
As for which platform to learn first, choose the one that both has a large number of job opportunities, plus seems the most fun and interesting to you. The last thing you want to do is switch careers to something that is boring and repetitive that you are going to hate doing for years and years, until you retire (or decide to switch careers again, because you hate it).
Good Luck!
