How can they be? I have been finding loads of information for me to think they can't be. For example....
Employment status: basic checks to help you decide
You can usually work out your employment status by asking a few straightforward questions.
You are probably self-employed if you:
run your own business and take responsibility for its success or failure
have several customers at the same time
can decide how, when and where you do your work
are free to hire other people to do the work for you or help you at your own expense
provide the main items of equipment to do your work
You are probably employed if you:
have to do the work yourself
work for one person at a time, who is in charge of what you do and takes on the risks of the business
can be told how, when and where you do your work
have to work a set amount of hours
are paid a regular amount according to the hours you work, and get paid for working overtime - even if you do casual or part-time work, you can still be employed

From hmrc website.

It's only really on here that I've seen people say they can be. So please tell me how as I would prefer to not have to pay out for things like pensions, holiday, sick pay and allow breaks....!