I had the exact same thing happen. I haven't claimed since my son started secondary school (he is now in sixth form college). I was above the threshold on income, but last year my husband had his PIP care allowance moved to top tier (he is on top tier mobility already). Payments started to go into my account, so I rang them and they explained that because of husband getting top tier care, I was entitled to the payments. Fast forward to this year, and low and behold, I owe about £500 and am not entitled to Tax Credits because of my income. I rang them this week and they said once you claim you are always in the system, and if your circumstances change Tax Credits entitlement will be reviewed (even if you weren't claiming, as in my case), and will be awarded accordingly. I pointed out this was a bit silly as I knew I was earning more than allowed. Upshot is I have to pay back the money (half expected that anyway), but I have asked to be opted out of Tax Credits so it doesn't happen again. As MartinMillar advises, I would put the money to one side, chances are you will need to repay it at the end of this financial year.