Exclusion of Basic Rate Pension tax relief in Self Assessment calculations

I have a query regarding Basic rate tax relief on personal contributions, which i believe are being excluded from the tax "reliefs" that are calculated via self assessment. I wanted to double check my understanding. To clarify what i mean above, if a higher or additional rate earner wants to reduce their overall tax burden, one way of doing this is via personal pension contributions (for instance via a SIPP, obviously within the limits of the annual allowance and carry-forward rules). Assuming relief at source, the basic rate relief is effectively claimed via the pension provider but the higher/additional rate relief is claimed via completing self assessment (resulting in an increase in basic rate banding and usually resulting in a refund from HMRC via self assessment assuming the earner is a salaried PAYE employee) I understand all of the above mechanics well, but if even more tax relief was desired on top of the pension relief one scenario is that the earner could look into making investments which result in an income tax rebate, such as VCTs, EIS or SEIS (or some combination of these). One theoretical scenario would be that the earner not only invests in personal pension contributions but also puts enough into VCT/EIS/SEIS to effectively achieve a 100% refund of all tax paid, via their self assessment.However i have noticed that interestingly the self assessment calculations don't seem to factor in basic rate relief received inside the SIPP, so effectively in the 100% refund self assessment scenario the earner is actually receiving a net tax credit from HMRC taking into account the basic rate pension relief? In this above scenario, is it right to think of that the basic rate tax relief claimed via relief at source in the pension is 100% still valid or could it theoretically be clawed back? My impression is that basic rate relief pretty much applies to all personal pension contributions (no questions asked) assuming a person is working and earning normally, with one argument being that the "relief" is there partly to encourage pension investment but it is actually excluded from self assessment calculations (one key reason for which might be that you are eventually subject to tax on the way out with the pension). Many thanks in advance for hopefully clarifying my understanding. I hope the above makes sense. I believe the above is

Hi,

You can see guidance on Income Tax rates here:

Income Tax rates and Personal Allowances

When claiming higher rate tax relief in your Self Assessment tax return, you increase the 20% threshold of £50270, by the gross amount of pension payments you made in the tax year.  By increasing the 20% rate, you are in effect reducing the highest rates of tax you pay by the same amount. This means you pay more tax at 20% and less at the other rates, thus giving tax relief.

If you claimed tax relief on EIS/SEIS shares, the Self Assessment tax calculation reduces your tax liability by a straight forward credit of the amount of investment at 30%, for example,  your tax liability is £20000 and you invest £33333 in EIS shares, £33333 at 30% is £10000. Your tax liability of £20000 is reduced by £10000, if you have paid more than £10000 tax, the difference is refunded to you.

Thank you.