Since January 2013 the high income child benefit charge (HICBC) is payable where a person, or the spouse or partner they live with, receives child benefit and one of them has income of more than £50,000 per year. The charge is supposed to be taken from the spouse/partner with the highest income.
HMRC has issued a warning letter to anyone in receipt of child benefit who had earnings over £50,000 in 2012/13, but who did not report the HICBC on their tax returns. The trouble is HMRC do not seem to have bothered to first check whether the HICBC had been correctly reported on the tax return of the partner/spouse.
HMRC are apparently aware of its error and so if you’ve received a letter, but are sure that you weren’t required to report the HICBC on your 2012/13 tax return, you can safely ignore it.