I've recently applied for Marriage Allowance as we're eligible while I'm on maternity leave. It's been backdated for the last tax year too. With my lower personal allowance I have now underpaid about £230 in tax and have received a demand. My DH has been told he has overpaid by £170. We are worse off by about £60. Is this supposed to be possible with Marriage Allowance, and if so can I just cancel it?