Backdated tax allowance

My wife stopped working in 2020 when she was 63. She started claiming her state pension last year at the age of 66. She therefore didn’t use her tax allowance from April 2020 to April 2023. She now wants to cash in her private pension and wants to know if she can use her unused tax allowance from 2020 to 2023

Hi,

The pension would be taxed in the tax year that the pension provider was due to pay them. 

Thank you.