Tax Credits are means-tested benefits for workers or families on a low income. They are administered and paid by Her Majesty's Revenue and Customs (HMRC).
Tax Credits are being replaced by Universal Credit. It is now only possible to make a claim for Child Tax Credit or Working Tax Credit if you already receive the other type of Tax Credit. You can update their existing Tax Credit claim by reporting a change in circumstances online or by phone.
Cross-border workers living abroad (i.e. the Republic of Ireland) but working in the UK can still make a claim to Tax Credits because they are unable to claim Universal Credit (UC), although they will first need to get evidence from the Department for Communities to show they are ineligible for UC.
More information about Tax Credits and how to contact HMRC about a Tax Credits claim can be accessed at gov.uk: