Your documents look fine to me
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I'm a bit worried there seems to be a lot of Natwest letters! Would these be counted as two separate sources (current account/savings account) or one as they are from the same bank? I do have another provisional list from Aug 2018-2020 in case there is something fundamentally wrong with this one?
Nothing to be worried about... as long as you have at least 2 other sources, it doesn't matter how many Natwest letters you have.
You only need 3 sources and you have 4 sources in total... and they're all evenly spaced, so your documents meet the requirements perfectly
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Anything from a bank counts as 1 source only, so the Natwest statements, Natwest letters and Lloyds account statement are all 1 source... but you also have 3 other sources, so no issues there.
So, as a summary, you have:
September 20181. Joint = Natwest Current Account statement (Source 1)
January 20192. Joint = Natwest Current Account statement
May 20193. Applicant = Polling Card (Source 2)
3. Sponsor = Polling Card
September 20194. Applicant: Nest Pension letter (Source 3)
4. Sponsor: Natwest Savings Account Letter
January 20205. Joint = Natwest Changes to Savings Account
May 20206. Joint = Natwest Current Account statement
August 20207. Applicant = Lloyds Current Account statement
7. Sponsor = Talk Talk bill (Source 4)