> I'll have to enquire with the few mates there
Sole traders are different to one-person Ltd companies. As a one-person Ltd, you used to get a lot of tax breaks, but over the last 5-6 years they seem to have been steadily eroded.
Anyone paying a rate as low as 13% now is probably using a borderline-legal grey-area scheme, which is dangerous because HMRC not only hit those folks up for back taxes when they find them, but put fines on top too.
I'll have to enquire with the few mates there -- don't see a reason as to why they'd bullshit me. Frankly I have nfi however, apologies for the cop-out of an answer.
1: https://www.highspeedtraining.co.uk/hub/sole-trader-tax/