Serious stuff this. Many years ago I had to travel the width of the UK to do my job flying and training crews in Cardiff. I claimed to be self employed and set all kind of costs against my income. Car and accommodation were of course the main items. I got a huge tax bill.
I went to what must have been the heavy end of a tribunal. A magistrate, a QC and two top tax bods. I went in alone.
This just was being employed to do a job for one employer over a year obliged me to be properly employed on a PAYE basis.
I protested long and loud for about an hour, citing all kinds of business done by one man bands. At the very least it would have opened up a huge can of worms and while waiting outside, one of the tax bods said, 'I think you've got this one.' I asked him if they'd appeal. He said no.
When I went in, the QC and magistrate had decided I could keep my money. It was a huge Phew! moment.
Later the law changed and who knows, it might well have been my argument that prompted it.
I was told by local tradesmen that one had to work for at least three employer/clients in the tax year to be considered for self-employed status. I never put it to the test, but what I did do was start a Limited Liability company in another trade. I also flew freelance 3 days a week.
I hired a respected accountant and he did everything. Really earned his keep.
Now, new dangers.
Just being one of the two (then a minimum number) directors left you open to 178 criminal laws. It is not a free lunch--despite how many free lunches you get.
It worked quite well for us, but there was a huge amount of paperwork involved with tax and VAT alone, and every invoice and slip of paper was a legal document, with all that implies.
Take care and keep a fat tax fund healthy and locked away from temptation.