Regular contributions to SIPP

I am a higher rate (40%) taxpayer and have been making regular contributions to a SIPP over the past 12 months. The basic rate tax relief has been automatically added by the investment management firm (Vanguard), but it will shortly be time for me to claim my additional 20% tax relief from HMRC. According to the HMRC guidance, I can either (a) complete a Self Assessment return from 6th April, or (b) contact HMRC to request a refund. Aside from seeking this additional tax relief, I have no other reason to require a Self Assessment return and so when completing the form "Do I need to complete a Self Assessment?", I invariably am informed that I do not need to do so as this form doesn't capture pension contribution tax relief. Therefore, my question is twofold - 1) What is the most suitable way of claiming this tax relief?, and 2) Can I decide how this tax relief is refunded (i.e. one-off payment or adjustment to future tax code)?

Hi crayby99,
Completing a Self Assessment tax return would make any repayment due available immediately.
If you have no other reason to file a return, though, you may find it simpler to write to us to claim the relief due.
Please confirm the amounts paid (with documentary evidence if those amounts are over £10,000).
While we can't give a timescale for when your claim would be processed, we do aim to process any post received as soon as possible.
Thank you.