Better-off parents affected by child benefit cuts need to "get off their backsides" and register with HM Revenue and Customs, its head warned on the the eve of the stated deadline.
Families were given until the end of tomorrow to opt out of receiving the state help or register for income tax self-assessment so some or all of it can be clawed back - or face possible fines.
Officials say that in reality punishments are unlikely to be imposed on anyone who complies by the end of January, but HMRC chief executive Lin Homer said many thousands had still not done so.
More top news
Theresa May will attend a key EU summit on Thursday, just hours after her authority was diminished by a humiliating House of Commons defeat.
The best of the sunshine will be in the east.
The British territory will allow only domestic partnerships after senators approved the Domestic Partnership Act by an 8-3 vote.