Tax rebate on missed years of claiming additional pension contributions payments

NYorks_

Hello,
just wondering if anyone would be able to explain how the below would work.
I'm a HTR payer since 2015 and have been contributing to my workplace pension scheme for years. However (and this is totally my fault for failing to be more informed!) I have only been claiming additional tax relief for personal pension contributions for the last couple of years (tax years 2019-2020 and 2020-2021). I understand that HMRC allows to claim additional tax relief on pension contributions retrospectively for a definite period of time. I think I might therefore be able to claim additional tax relief for 2 (or 3?) further years back prior 2019, and that I need to send HRMC a letter explaining the figures (salary and personal pension contributions). This is fine, all clear, however I'm confused on how the tax rebate (if and when given) would work. For instance if it's a change in tax code, and given that we are nearing the end of FY 2020-2021, would there be a change in code to confine the tax relief to the remaining months of FY 2020-2021 or will the change in tax code be affecting FY 2021-2022? Or if the rebate is not given by a change in tax code, how will it be?
Hope this is tot too confusing - thanks in advance  

Dazed_and_C0nfused

Firstly HMRC never allow tax relief on pension contributions in a different tax year to the tax year the contribution was paid in.  So it isn't possible to get tax relief through your current or next year's tax code.

Any tax relief due for tax years prior to 2020:21 would be refunded direct to you by HMRC (either by cheque or them inviting you to pull the tax overpaid into your bank account).

You can claim back to the 2016:17 tax year.

Have you completed Self Assessment returns for any of the tax years involved?

Are your contributions made using the relief at source method?

NYorks_

Dazed_and_C0nfused said:

Firstly HMRC never allow tax relief on pension contributions in a different tax year to the tax year the contribution was paid in.  So it isn't possible to get tax relief through your current or next year's tax code.

Any tax relief due for tax years prior to 2020:21 would be refunded direct to you by HMRC (either by cheque or them inviting you to pull the tax overpaid into your bank account).

You can claim back to the 2016:17 tax year.

Have you completed Self Assessment returns for any of the tax years involved?

Are your contributions made using the relief at source method?

Thank you DaC for your reply, clear on the different tax years, thanks.
To answer your questions:
- No, I have not completed a Self Assessment before - should I now to start the refund process? My understanding is that a letter to HMRC with the details should be sufficient? Of course I might be wrong here.
- Yes I believe that 'relief at source' describes my situation (my own pension contributions are taken AFTER tax is deducted, as my employer does not offer a salary sacrifice scheme...I know we have asked but to no avail..)
Many thanks

Dazed_and_C0nfused

No, there is virtually never any need to complete a Self Assesment return just to claim higher rate tax tax relief on pension contributions.

But if you had completed one the process to make a claim is completely different.

I presume you are aware of this but there is no "extra 20%"' with relief at source at source pension contributions.  A common misconception on here. 

The gross amount simply increases your basic rate tax band which in turn can reduce the amount of tax payable at 40%.  You will see this on the calculations HMRC issue.

But if you have only paid higher rate tax on say £10 of your income the higher rate tax relief due would only be £2.  Even if you had contributed say £10k (gross) to the pension.