So to be deemed as ‘outside IR35’ will I need to show I am in business on my own account (effectively self-employed)?

For IR35 to apply you need to be regarded as an employee of the end client. So conversely to be outside of IR35 legislation, you need to show that you are not an employee of the end client.

This is not the same as showing you are self-employed; although being able to demonstrate you are in business on your own account is always regarded as the best option.