I never knew any farners who admitted to being rich in moeny terms

And I met quite a few in my working lief!
Quite a good site and good advice on contacting HMRC local office sooner rather than later if you are in any doubt. They really re much more approachable nowadays!

Tax payable is a percentage after the deduction of your personal allowance, so if you earn £100 more than before you will pay the same percentage tax on that £100 as on the previous £100.
eg for the current year to 5th April 2012
Total income £10000, as earned up to 16th March
Personal allowance for the whole year £7475
Taxable income is therefore £2525 taxed at @ 20% = £505, so you are left with £9495 up to 16th March
If you earn £1000 from 17th March to 5th April you would pay tax of £200 on it at 20%, so all in all you have earned £11000, paid tax of £705, and have a net income after tax of £10295 The extra tax is 20% on whatever is earned - it does NOT increase proportionally
Then there is National Insurance but I won;'t go into that just now as it is much more complicated.
And this is EXACTLY what I have said previously -
USING eBay
All that seems very clear and simple, but then it gets a bit trickier. For those who use eBay, or other listings sites, to make extra money it can be difficult to distinguish between using the site to earn an income and using it merely to get rid of some junk. As Jane Moore from the Institute of Chartered Accountants puts it: “Cash in the attic is not taxable, but the Revenue will know the difference between a clear-out and a small business.”
So if you are selling on unwanted items every now and then, in theory you are liable to be taxed on any profits, but usually small earnings will be ignored.
However, if you start to buy products to then sell on, or you are regularly selling large amounts of your possessions the rules change. Again, if your profits using listing sites or classified adverts, plus any other income/salary, do not exceed the £7,475 personal allowance in one year, you do not have to pay tax. But, if you make profits that exceed your personal allowance, or are an income on top of any salary or any other money-making, you should be declaring them as they are taxable.
Regularly buying items to sell on at a profit on eBay or other sites is in effect a small business, and so it is very important to keep a tab on profits and maintain clear records, including receipts of all your expenses which can be put against your profits for taxable purposes. This way, HM Revenue and Customs will be able to accurately calculate how much tax you owe and you won’t end up paying too much. But if you do find yourself going from selling a few things here and there to developing a small business, then you must let the Revenue know within three months. Otherwise you are liable for a £100 fine.