Three million taxpayers will be sent letters in the autumn asking if they or anyone in their household receives child benefit - so that it be taxed from January 2013.
The tax authorities will be targeting those earning around £50,000 a year and above. They will have to fill in self-assessment tax forms so that the benefit can be clawed back.
Those earning between £50,000 and £60,000 will lose a gradually increasing share of the benefit. Higher earners will lose it entirely.
The income tax charge could be levied from monthly pay cheques, via people's personal tax codes. Otherwise, the first tax bills for child benefit will have to be settled by the end of January 2014.