Have you set up a Personal Tax Account?

Your Personal Tax Account (PTA) can be set up and accessed via the GOV.UK website. Once your PTA has been activated you can use it to do the following:

checking Income Tax estimates and tax codes

completing and viewing a personal tax return

claiming a tax refund

managing tax credits

state pension information

track completed tax forms

check Marriage Allowance and updates

update HMRC on new contact information, such as a change of address

check/update working benefits, such as company cars and medical insurance

To register for your account you can use the Government Gateway Account which is provided by HMRC online services. Or, more recently, you can register using your National Insurance number and P60.