I have been in this situation and if it is only £50 a month then you just need to call them up and they will take those earnings out of your tax-free allowance, and won't necessarily have to change your tax code or register you as self employed. But call them up for clarification.
Hi there, any advice much appreciated. I work full time as an employee but have been asked to do some private work too-however this will only be £50 a month. So do I have to register as self employed to do this? If so how? No idea where to start atall!