It is not the first time that irregular payments were made.

BBC: NI Fire Service paid unapproved bonuses to three staff

While official statisticians have sorted out the main defects, irregular bonus payments continue to make the index volatile and largely account for the recent collapse in the growth of earnings.

ECONOMIST: Interest rates

"Personal income in November and December was boosted by accelerated and special dividend payments to persons and by accelerated bonus payments and other irregular pay in private wages and salaries in anticipation of changes in individual income tax rates, " the Commerce Department's Bureau of Economic Analysis said.

BBC: US personal incomes jump ahead of New Year tax rise