I also agree with this. Not a particular dig at you OP, it's a common way of phrasing questions on here that makes no sense whatsoever.
I'm a similar age to you, but otherwise my work circumstances are completely different. I earn a decent salary that is pocket change by MN standards but I have a science degree, 3 professional certifications and nearly 30 years experience in a very niche (genuinely!) area.
What I do and how I've got here isn't going to help you charge more for what you do, because it would take you a good 10 years to get anywhere near where I am even if you were a lot more pushy than what I've been.
You have to bear in mind that NMW is now £21k pa, so for self employment to be worth it, you need to be earning well above this to account for the fact you have no employer pension contributions or holiday or sick pay. You also have to use the experience and talents you already have, or else you've got to build in retraining time.
Can you get some employed work and do your SE work on the side as a hobby that provides an income? Can you just put your prices up? Make efficiencies to make more things to sell (hard to say without knowing what you do). Or you need to market yourself better to sell more of your product/service.
The other way would be to get into something with a training period in weeks/months not years, before you could start earning properly. So that could be something like HGV driving - does that appeal?
You say you have 20 years experience in the workplace - if this is different to your SE work, is it something you could go back to?