If you are a volunteer, or engaged by a charitable or voluntary organisation, notional earnings cannot be assumed if it is reasonable for you to provide your services free of charge. (A carer may count as a ‘volunteer’ – see CIS/93/91 , but see CIS/701/94 for exceptions.)

If it is reasonable to expect you to charge for your services, or you are performing a service for someone else in some other capacity, you are treated as having such earnings that are reasonable for that job. This will not apply, however, if the decision maker is satisfied that the means of the person you are providing the service to are insufficient for them to pay, or to pay more, for the service. Decision makers are advised to assume earnings of at least the relevant national living/minimum wage.
HB Regs, reg 42(9) &(10)(a); Decision Makers Guide, Vol 5, Chap 26, para 26180