How will I know my tax code has been changed to D0?
HMRC will send out a coding notice to you in the mail each time your code changes. The payroll department in your employing board may also notify you of this.
You may find out because your net pay is much lower than you are used to as you will be taxed on your full salary, at 40% higher rate tax.
When you notice you have paid a lot of tax please call HMRC as soon as possible to ensure this change can be processed in your next months pay.