This means he will be paying more tax in the current tax year than he did last tax year - at basic rate, it will work at at just over �150 a year extra. His tax code could be reduced for a number of reasons - the receipt of other untaxed income, benefits in kind (such as a company car) or the collecton of tax underpaid in earlier years. He should have been sent a coding notice, which will show how the code is made up. If he has misplaced it, he can ring his tax office and they will explain the code to him.