Just purely from the tax point of view, HMRC rules have changed many times over the years. More recently they have become very much accepting of the fact that many people occasionally sell the products of their hobbies without looking to make a profit. Such people are not considered to be 'trading' in the context of the relevant leglislation. They accept that requiring such people to register as sole traders is not sensible. In particular they say that you will only be considered to be a 'trader' if you:
- sell regularly to make a profit;
- make items to sell for profit;
- sell online, at car boot sales or through classified adverts on a regular basis;
- earn commission from selling goods for other people;
- are paid for a service you provide;
They also specifically say:
"You’re probably not trading if you sell some unwanted items occasionally or you don’t plan to make a profit. You can’t use any losses you make as part of a hobby to reduce your tax bill."
In addition, you don't need to register as self-employed if you earn less than £1,000 from self-employment in a tax year. If you are also 'employed' in your main job, that income is treated separately
unless you qualify as a 'trader' (as above), in which case all income is considered a whole when assessing tax liability.
So under current legislation there is definitely no requirement to disclose any information to HMRC if you are selling product but not looking to make a profit.
https://www.gov.uk/working-for-yourself