Inquiry Regarding Withholding Tax Information Between UK and Spain

I am reaching out to inquire about obtaining information on withholding tax requirements between the United Kingdom and Spain. I am interested in understanding the regulations and procedures regarding withholding tax obligations related to transactions between these two countries. Could you please provide guidance on where I can access relevant information or documentation on the withholding tax agreements and rates applicable to transactions involving the UK and Spain? Your assistance in directing me to the appropriate resources or providing any pertinent details on this matter would be greatly appreciated.

I would appreciate some guidance on the procedure to follow for UK residents who are interest payers. Starting from 1 January 2021, UK resident interest payers must determine if the domestic rate can be reduced or eliminated under a double tax treaty between the UK and the recipient's territory of residence. If a reduction is applicable, the UK payer must apply for and seek direction from HM Revenue & Customs (HMRC) to pay the reduced rate before making any payment. I would like to know the specific steps and requirements for this process. Thank you in advance for your assistance.

Hi Rcarde,
If you are a UK resident and have overseas interest, which will be taxable in the UK, you can contact HMRC and request a certificate of residence to present to the country in question, provided there is a tax treaty between both countries.
Have a look here:
How to apply for a certificate of residence to claim tax relief abroad
Thank you. 

Hi Rcarde,
Please refer to the UK/Spain double taxation agreement on the gov.uk website at:
2014 UK-Spain Double Taxation Convention
There is also information in HMRC’s Double Taxation Manual at DT17550PP, weblink here:
DT17550PP - Double Taxation Relief Manual: Guidance by country: Spain: Contents
Thank you.