When to register as self employed

BriNylon

Am I right in thinking that you need to register as self employed by 5 October after you become self employed?
when do you actually become self employed?  Individual started a hobby. Then started selling items.  Then started teaching others. Looks like this year they will exceed 1k. 
If they had turnover of over 1k last year but expenses were over 1k, so there was a loss, would they be self employed?  It was a hobby. Just morphed into making money from it,  

Jeremy535897

If you are running a business, and your turnover exceeds £1,000 in the tax year, you should register as self employed by 5 October in the second tax year in which you traded. For example, start trade 1 July 2023, register by 5 October 2024. There is absolutely no benefit in waiting. Register as soon as possible.

For a discussion on HMRC's view of when trading starts, see:
https://www.gov.uk/hmrc-internal-manuals/business-income-manual/bim80505