If you are presently eligible for working tax credit/child tax credit you may be affected by the changes due to take place wef 6.4.12.
This link should give you some info.
http://www.direct.gov.uk/en/MoneyTaxAndBenefits/TaxCredits/DG_194914
Note the new rules for the increase in hours needing to be worked (minimum of 24 per week in total) for a couple to be able to claim working tax credit. Hours for a single person (minimum of 16 per week) stay the same.
As I understand it, if the couple fail to work 24 hours per week between them - could be just the one doing 24 or 10 by one and 14 by the other for example, like even by 30 minutes, then they will lose all their working tax credit and it is this aspect of the changes that has been causing a lot of controversy.
Please