As of 2016, 83 countries including the UK and Spain signed an agreement to implement a system for the automatic exchange of tax and financial information on a global level.
It is common for UK banks to send letters to account holders who have given their Tenerife address as their residence address.
The letter asks for various information and the format varies slightly between the different banks, but the gist of the letter/form is that you need to provide your country [or countries] of Residence for Tax Purposes so that they can share information between countries so that correct taxes are paid.
The letter asks for, name, address, date of birth, “TIN” (Tax Identification number) and countries of residence with from/to dates. If you are FISCALLY Resident in UK then the TIN is your UK national insurance number, but if you are fiscally resident here it is your NIE number.
The letter will state a reply cut-off date otherwise they say they will pass details to the appropriate tax authorities.
This letters are being generated as a direct result of the Common Reporting Standard (CRS) which is a system for the automatic exchange of tax and financial information on a global level, developed by the Organisation for Economic Co-operation and Development (OECD) in 2014. Its purpose is to combat tax evasion. Its legal basis is the Convention on Mutual Administrative Assistance in Tax Matters.