Dont even go there.
I have had so much hassle with the Tax Credits people since they started it is beyond a joke.
Every year i tell them what my OH earns, and i tell them of changes in circumstances as they happen, without fail. And yet i still get overpaid when i complain or make enquiries i get no-where, one minute there saying its your money, the next it's oh nope sorry we were suppose to stop paying you x amount of months ago.
It is total madness. I personally owe them £1700 so far. I cant pay it back. OH has just started doing ovetime at work latley too so i phoned them and told them. I thought i'd ask them while i was on the phone what is the maximum amount of money we would need to earn to get off the credits.
erm

for 2 adults and 2 children in our situation our combined income has to be £58 thousand

at least. We have no chance.