HMRC guides UK eBay traders on income tax
Seems that if you just use eBay to get rid of unwanted gifts or purchases, the mighty hob-nailed jackboot of the taxman (or 'HM Revenue and Customs' if you prefer, your majesty) will refrain from crushing your tiny profit and demanding its 25% (or 40%) cut on each sale. However, if you seek to make a profit by listing goods you bought with the sole intention of reselling them, then you're liable for the tax.
Well done. Sense prevails. For once :)