the rules have not changed at all just drawing peoples attwention to the fact that you can't have a trading buisness and just pretend you don't
supposing you have a mulberry handbag that you paid £500 for 15 years ago, even if you sell it for £800 and make a profit this is not trading vecause it was your personal possession so the £300 profit is tax free no tax return required. however if you bought a diamond necklace 15 years ago for £3000 and sold it for £13000 you have made a capital gain of 10,000 that requires a tax return but you have a capital gains allowance and can use last year's too as well
however what is more likely is that you bought a coat 2 years ago for £200 and you now sell for £60 so you have not made £60 it is actually a loss of £140 so again no tax return as it is not a profit and it was your personal possession. The vast majority of stuff sells for less second hand than inital purchase price so no worries for 95% of people selling their own unused items
however if you spot some items at a car boot sale that you realise are undervalued maybe old marvel comics or art deco bakelite jewellery so you buy it and then resell this is trading and you have a personal trading allowance of £1000 a year so if you sell on a few say 3 brooches that you paid £5 for r £75 each you have a profit of £210 well within limits so no bother
I am used to this as I have 2 ebay accounts one is my declared sole trading business account where I buy and sell vintage collectables and ceramics from auctions clearances etc and sell on for profit I sell more than £1000 and do a tax return and pay tax on it I also keep records of expenses as I obviously as a business can deduct what I paid for them, the fees charged by ebay postage , buying boxes bubble wrap packing peanuts etc, my car is registered as a business so I can claim for mileage going to auctions or going to post office.( you can't claim car or travelling costs if not a business) my other account is where we buy and sell our own stuff, it doesn't matter if it is over £1000 a year as it is our stuff not bought to trade. I make sure we don't mix accounts up they have very different names etc
ebay do monthly summaries it says the total sales how much your fees were and postag eif you buy it on ebay so it is easy to see what is what. if you are trading definitely get a second account