Certificate stating no uk resident tax liability

I am a UK citizen living and working in Spain for the last 35 years and i'm classed as a non UK resident for tax purposes and therefore do not pay any tax in the UK. I am entitled to a UK company pension fund for the years that i worked in the UK before moving to Spain. As i am reaching retirement age i have contacted the pension company and that have asked me for a certificate or document where it clearly states that i am not liable to pay tax in the UK. How can i request such documentation?

Hi Robert Nicholson,

HMRC do not provide certificates confirming that you are not resident in the UK, only that you are resident.  
To claim UK tax exemption on your pension, you should submit Double_Taxation_Spain_Indiviual.pdf (publishing.service.gov.uk) to us once your pension has commenced.  
You should send this to us with your certificate “Residencia Fiscal en Espana Convenio”.  
Please note however that certain pensions remain taxable in the UK and cannot be given the NT (No Tax) exemption.  
The attached link refers.
DT claims and applications - Types of income: Pensions and Annuities - HMRC.

Thank you.