Find another company to work for and then have a Chinese wall between work and home. Non-competes are basically illegal in the UK and most employers should be able to say “don’t work on X areas”. Remind them that work you do in your own time will benefit them as well.

I have none of my personal project code on my work laptop, I’ve never searched or thought about personal project work on it and I never take professional development time in work hours (unlike many other members of staff).

I’m at work to work for the company, I’m at home to work on myself. I never blur the lines, the downside to this is that my employer massively benefits from my time investment at home but oh well, it makes me better at my job and so I’m happier.