What I find absolutely astonishing, and a no brainer in the real status of your employment, is when friends of mine tell me that even though they are 'self-employed' they have to ask permission to take time off. That is true of even single days and/or a week; even with 2 months notice. Mostly, especially in summer it is refused. Doesn't sound very 'self-employed does it?
You can use this to your advantage in limited circumstances. On pilot I know employed his wife (who kept her maiden name) as his company secretary. When he decided he'd had enough and got another job and decided that as a contractor he was no longer contracting to RYR, they only had her number (a pay as you go number only for RYR use) and weren't too happy to be told that his services were no longer available.