I don't think you can really run a so called successful business for less than £50 per hour and even that is treading a very thin margin. There are "plenty" of subby jobs out there within 1 hours commute of most places in the UK where rates of £25-£30 are realistic.
If someone can tell me they can cover the extra costs between being a subby with a basic set of tools and no need for a van/test equipment/nothing more advanced than a drill, plus they don't need scheme membership, - if you can cover that plus all the "free quotes/ insurances fuel/admin time" for £20 per hour then you are doing bloody well, I base the £20 per hour as you can easily get £25 within commutable distance then £45 is really right...so is £50 when you can get £30's within commutable distance.
I mean obviously there is more to life - some people such as myself enjoy total freedom and only do 2-3 days per week, But I achieve this by being expensive lol. But yeah some just love the freedom, Others can't stand working under any sort of supervision...again fair enough, But one must be careful not to actually end up effectively "paying" to be a sole trader. It's a fools game, Nobody will care when you have that bit of bad luck that kills your whole business stone dead, IMHO if you are charging <£45 you are an accident away from financial distress/ A couple of thefts away from the same, A slow paying customer away from similar. Businesses are actually "supposed" to make a profit AFTER wages and expenses are accounted for.