From the financial requirement guidance document:
One of the following documents must also be provided:
• a certificate of VAT registration and the VAT return for the last full financial
year (a copy or a print-out) confirming the VAT registration number, if turnover
is in excess of £79,000 or was in excess of the threshold which applied during
the last full financial year
• proof of ownership or lease of business premises
• original proof of registration with HMRC as an employer for the purposes of
PAYE and National Insurance, proof of PAYE reference number and Accounts
Office reference number. This evidence may be in the form of a certified copy
of the documentation issued by HMRC
My understanding of that is that if you have provided a document falling under one of the first two bullet points, you would not need to provide a document falling under the third bullet point. If you are relying on a document falling under the third bullet point to meet this requirement, I can't help much more beyond what is stated in the guidance as to where to get this as I would assume it would have been provided by HMRC at some point if it was necessary for them to do so.
https://assets.publishing.service.gov.u ... .0-ext.pdf
I'm just a guy on the Internet who immigrated to the UK. My opinions are based on my experience and interpretation of the immigration rules and should not be considered legal or immigration advice; your mileage may vary.