HMRC has sent out thousands of incorrect tax statements, and made refunds of tax that are wrong.
Time and again I have said you cannot run a tax system on the cheap and that such a system does need plenty of highly trained people who have a very accurate sense of what might, can and does go wrong.
HMRC is being denied those resources. Don't blame them for the current mistake.
The blame lies fairly and squarely at George Osborne's door.