How are tax underpayments collected by HMRC?
You might not always pay the right amount of tax in a year. You can have particular problems if you have several sources of income.
As we have explained, the armed forces collect tax from your salary throughout the year via Pay As You Earn (PAYE). If you have had a single employer throughout the whole tax year and little other income, then often you will have paid the right amount of tax when the tax year finishes. In some cases this does not happen, for example when you have two jobs and/or pensions during the tax year. If you have underpaid tax, HMRC will ask you to pay what you owe.
There is a guide in the employment section of this website, which tells you what to do if HM Revenue & Customs (HMRC) think you have not paid enough tax for a year. See What if I do not pay enough tax?.