You need to tell HM Revenue and Customs (HMRC) if your additional income hasn’t been taxed through either:
•your main job
•another Pay As You Earn (PAYE) scheme
This is called a ‘voluntary disclosure’. To get the best possible terms you need to tell HMRC that you want to take part in the campaign.
You’ll have 4 months to calculate and pay what you owe.
You can find out about the campaign and how to make a disclosure here
The criteria used to assess if an activity is a hobby or a business are:
•The size and commerciality of the activity.
•The frequency of the activity and transactions
•The application of business principles.
•Whether there is a genuine profit motive.
•The amount of time devoted to the activities.
•The existence of arm's-length customers (as opposed to just selling your wares to family and friends).
If you have a Second Income its better to disclose it now rather than wait till HMRC find you.