UK rental income

Hi everyone we plan to move to san pedro area in the next few weeks and proceed getting all are paperwork in order so we have all requirements met by the 31 December. I am going to rent out my UK property while out in Spain. I'm getting confused with all the taxes in Spain. 

So as an example say.... 

£7200 rental UK income a year starting August 2020. When do I declare the money earned upto end if tax year and which country do I declare it in 1st, secondly is it the model0 720 form for the other declaration of overseas assets in wealth tax or will I get taxed another way

Thanks Adam