You can check your entitlement to Working Tax Credit and apply online here or order a claim pack by phoning the Tax Credit Helpline on 0345 300 3900. This line is open 8am to 8pm Monday to Friday, 8am to 4pm Saturday and 9am to 5pm Sunday.
Guidance from HMRC (leaflet WTC2) points out the important differences between claiming as a single person and claiming as a couple, so that you don’t make a mistake and accidentally build up an overpayment or incur a penalty.
You must claim as a couple if you’re married, living with someone as if married, in a civil partnership, or a couple living apart temporarily. If you don’t have a partner, you should make a single claim based on your circumstances.