Dear Masquette,

Welcome to the belegal forum.

Let me just start by explaining that once you live in Spain for more than 183 days per year, you became a Spanish fiscal resident and that you can only be a fiscal resident in one country; not in two.

Once you become a fiscal resident in one country you are in the obligation to inform the tax authorities on your income all over the world.

In Spain , as in the UK , you can be a salaried worker in a company and work as sole trader at the same time. In this case, there will be two social security contributions and you will be liable to pay taxes for both activities. These social security payments are independent from each other and are not considered a double payment, however, at the end of the year when the self-assessment form is filed, those are expenses fully deductible from any income you may have had on that period.


With regards to issuing invoices with your UK national insurance number, I am afraid that this is not possible. You will need to be a registered sole trader in the UK or here in Spain in order to issue invoices. If you are registered in the UK you will have a VAT number assigned and in Spain a NIF ( Numero de Identificacion fiscal, that is normally the same number as your NIE Number).


I believe that your issue is much simpler than it seems: You live in Spain , work for a Spanish company and in addition you have the chance to get additional income with your extra work.
Establishing an international company ´s structure may be a step you can think of once the business has fully taken off. In the meantime, the easier and cheaper option is to keep your affair within one country , Spain or the UK.

You need to consider that registering a company ( in UK or Spain ) would also mean you have to get assistance from an accountant in the UK that will file accounts at the Mercantile Registry as well as the Inland Revenue and that entails costs.

At this point the main issue you would need to consider is whether to register as a sole trader or create a company, and that will be based on the income you make. If you estimate a net income of over 50.000 euros a year you should start thinking about creating a company; if less than that, to register as a sole trader is the most convenient option.


Regards,