The CoP have approved this type of payment before it's called a Family Care Payment but it does have other names often a Gratuitous Family Payment or similar. See link below.
The Inland Revenue recognise this as a tax free gift and it does not attract income tax, national insurance and does not confer any employment rights or liabilities.
Some may argue that in the cases that went before the CoP the person in reciept of the payment was a CoP deputy, but if you read the judgements then it was never made a condition that you had to be a CoP deputy, however, as Nitram says it may be wise to tell the CoP and clear it with them first.
If you google the phrase "Gratuitous Family Payment" you'll find a lot of information from various sources, some relate to people with AZ, some to people with acquired brain injuries and several other reasons. As far as I can see it has never been refused it's more about what is a "reasonable" amount.
K
https://www.gov.uk/government/publications/public-guardian-practice-note-family-care-payments