A survey cited by the Sunday Times claims as many as 8 million people buy and sell items online. That’s twice as many as the number officially self-employed, so it may be that many of these people haven’t yet registered with the taxman. The self-employed section of the HMRC website sets out the basic rules – for example, you need to pay Class 2 NI contributions to qualify for the State pension. It’s important to remember that because you pay income tax (on your profits) in arrears, you need to set aside money for the tax payments that become due at the end of January and July.