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.