Readers’ forum: When does a hobby become a taxable trade?

I have a client who is a well-paid local government official. She has always been a keen amateur photographer and has from time to time received small sums (never more than a few hundred pounds a year) for her photographs. I’ve always taken the view that this is a non-taxable hobby and in any case would be covered by the trading allowance. No notification has been given to HMRC about this activity. She has told me that she is starting to become well known in her locality and is likely to receive more substantial income from photography in the future to the extent that she may well change to part-time employment to have time to develop her photograph businesses.

At what point does this turn from a hobby into a taxable trade and if and when it does what is the capital allowances position on the cost...