The Spanish love their bureaucracy and it can be quite bewildering for non-Spaniards to understand, especially if you are not familiar with the language

To live in Spain, you will require the following

NIE (Registration number for foreigners). Without this, you can get very little done in Spain. It is free and the number stays with you for life. It is obtained from the Policia Nacional that serves your town

They will give you two forms to complete, one of which is to pay the certificate cost of €10 at a bank

You would need to take your passport (+ copy)
Passport style photo

Padron (shortened by both the Spanish and foreigners (that means us!) from “Empadronamiento”. It is a local census. This document is provided when you register at your local Town Hall (Ayuntamiento). It should be periodically renewed. It is free

You would need to take your passport (+ copy), copy NIE certificate plus one of the following

Utility bill

Copy escritura (property deeds)

Copy of a Rental agreement

All people who live in Spain whether natives or not are required to register. This proves where you live, but more importantly is needed to gain access to the health and education systems. It is also needed for larger capital purchases, such as a car and in many cases when re-registering your vehicle

In a wider context, the local area is provided with funds from upper levels of government based upon the amount of people registered

It is vital that you obtain an “historical Padron”. This shows both the date of application and the date of issue in separate places. When applying at the Ayuntamiento, you would need to explain that you need it because you are moving to Spain (even if will only be a “part-timer”) and importing your personal vehicle.
In most cases, a Padron is not required in order to re-register a vehicle

Certificado De Registro. (Certificate of Registration). This document replaced the previous ID card called a Residencia. Basically, it is a national register of foreigners in Spain and is useful when dealing with the bureaucracy. You are supposed to obtain one within 3 months of arriving in Spain if you are permanent here. Costs about 10 euros. This is normally not needed to re-register a vehicle

None of the above documents make you a fiscal resident of Spain, so you need have no concerns about paying extra taxes, or losing your UK rights

Whilst I am not an expert in all of these areas, as an expat who deals with the Spanish daily and can speak the language, I have gained an understanding, so if I can give you any help, please ask