Yet another change going on. If you sell quite a lot, meaning over 30 items in a year which appear to be new, they require your National insurance number to forward to HMRC. Once i have sold what i have in stock, i am not going to sell any more parts. It was a bit of a hobby and been selling for 20 years but i can live without the tax man coming knocking.
Selling old rubbish from your house and clothes etc will be OK and not taxable