I am not an accountant, but I do run a business in the UK and my understanding is that it's a threshold thing, which I believe is £2,500.

Assuming you don't currently have to submit self assessment, and your additional income from all sources other than employment (for which you already pay tax) is less than £2,500, you don't have to declare it.

Above this level you have to submit self assessment.

More information can be found here

I also find that HMRC are quite helpful - give them a call and ask.

Not sure about the UK, but if it were in the US you need to realize the expenses can be claimed as much as the income.

After having a mild heart attack when I did my business taxes the first time many years ago, a Small Business Administration adviser pointed it out.

You are running the site from a computer? Deductible on an amortization schedule. Do you work from home? Electricity can be deducted. Do you drive at all? Did you pay yourself a wage? Any paperwork, fax communications, bank fees that you had to endure as work expenses?

I am not an accountant, but chances are you legally lost quite a bit more than you made in a new web venture. Discuss it with an accountant for the details and more importantly the laws in your country. I could be off my rocker.

Income is income... it depends how it's structured.. personal or corporate.. but still you need to pay taxes... if you get audited, the tax man could look at your bank statements and ask, "where is this money coming from"