Cash in hand jobs

[LuckyManifestations]

If I hear of someone looking for 'cash in hand' work, I always presume that its a side line for them, a bit of extra cash earned on the side, or a top up to their pension/UC etc.

I heard today of someone working full time and being paid cash in hand. Is this really a thing?
Do you think its a large amount of people who do this? Or is it more likely to be as I said in my opening sentence?

Are they self employed or working for a company?

Working for a company as far as I know. The people concerned weren't speaking directly to me, I just overheard the conversation, and thought it would be rude to ask.......although I was dying to!

Quite a lot. In industries like beauty, hairdressing, take away, small shops. Basically anything with a high cash flow

I must be very naive