Hello diggit4..
...I don't know either...
You could phone your tax office and ask them..they're usually helpful...honestly...
It could depend on the amount of hours you work..how much you earn..etc.
I wondered if you are claiming Carers' Allowance ?
To be honest the Benefits System/Tax System is so complicated these days your best bet is to go directly to them and ask their advice.
Sorry not to be more helpful..
Let us know how you get on.
Love gigi xx