They are considered to be self-employed. If they're earning more than £1000 a year, then they need to file a self-assessment tax return with HMRC, and if they're earning more than a certain amount, perhaps £12500 a year, they will need to pay income tax on those earnings (plus national insurance).
Do most gig workers actually do these things? I have no idea.
Do most gig workers actually do these things? I have no idea.