I have just read that H.M.Customs & Excise are going to crack down on British people who are selling a lot on Ebay without declaring they are running businesses or making large profits.
As from 1st August Ebay are going to hand over records of members names, addresses, phone numbers, user names and records of sales and amounts that have been made as profits.
There will be an amnesty for sellers until the 1st August where if a seller declares to the Tax people the profits he/she has made on Ebay only 10% tax will be charged. If sellers don't tell, the tax charges between 35% and 100% will be made, with no redress.
Apparently, the Tax people in Australia and Canada have recently done this with a lot of success.