If you add together all his income from pensions and earnings, take away tax free allowance which would have been on his advice of tax code last April, that will leave you with the amount you need to pay tax on. Multiply this by the 20% tax rate. You will then be able to see from P60 how much he actually paid and check if the amount they have quoted is correct. From past experience if you then contact the tax office and ask them to adjust his tax code to repay over a period of time they should agree.