Just got this from tax credits website.
What hours do you need to work?You don't have children
If you're not responsible for children, you need to work the following hours to get Working Tax Credit:
* if you're aged 25 or over, you need to do paid work of at least 30 hours a week
* if you have a disability and are aged 16 or over, you need to do paid work of at least 16 hours a week
* if you're aged 60 or over, you need to do paid work of at least 16 hours a week
How to work out usual working hours for your tax credits claim
You have children
If you're responsible for children you need to be aged at least 16, and work the following hours to get Working Tax Credit:
* if you're single, you need to do paid work of at least 16 hours a week
* if you're in a couple, your joint paid working hours need to be at least 24 a week, with one of you working at least 16 hours a week
So if you're a couple and only one of you is working, that person will need to work at least 24 hours a week.
If your joint working hours are less than 24 a week, you can still get Working Tax Credit if one of the following applies:
* one of you is aged 60 or over and working at least 16 hours a week
* one of you is disabled and working at least 16 hours a week
* one of you works at least 16 hours a week, and the other is entitled to Carer's Allowance - even if they don't get any payments because they receive other benefits instead
* one of you works at least 16 hours a week, and the other is 'incapacitated', an in-patient in hospital, or in prison (serving a custodial sentence, or remanded in custody awaiting trial or sentence)