You are dual tax resident. You will still need to submit SA109 and claim personal allowances (box 16 & 17) and the section for residence in other countries.
The completed form DT individual (Double Taxation: UK - Spain (Form Spain-Individual)
) will need to be sent to the Spanish tax authorities before being sent to HMRC. Please include the completed form HS304 (Non-residents tax relief under double taxation agreements (Self Assessment helpsheet HS304)
) with your tax return.
You will be required to complete SA106, to declare all of your overseas income and tax.
You will be able to claim a foreing tax credit, so you do not pay tax on the same income twice.