Spanish taxes and British taxes

As far as I know there is avoiding double taxation agreement between UK and Spain. I have always heard that a holiday home rental tax should be paid in the country where the property is located.

However recently I have read that holiday rental income from abroad has to be declared in British self-assesment. The problem is I cannot see on self-assesment form where you can declare the tax you have already paid abroad. There is no such thing at all.
So does it mean one will be taxed twice?

There always used to be an area on the self assessment form to add tax paid abroad, as I used to do mine several years ago. I haven't rented out for a while so got taken off the SA requirments, so the form may have changed.

Mark

Unfortunately they have a tendency to change forms and other items in your Personal Tax section on HMRC website every year now...
I've been doing self-assesment for about 12 years now and recently there are still things that surprise me. 

Unfortunately you are correct in as much as rental income is taxable in both countries. Following UK leaving EU you can no longer deduct expenses from the revenue figures in Spain. However although you must declare your income to HMRC you are able to deduct tax paid in Spain as well as expenses. You will attract tax on the net figure.

hope that helps.

As far as the UK tax man is concerned, and of course if you bother, he likes you to tell him of any change in curcumstances to your income, then up to him if you should pay tax or not, but if you do tell him they then know your income.

I know that I am not able to deduct tax paid in Spain as well as expenses. But it wasn't a question.

 
"You will attract tax on the net figure." So you guess - or you really know (and your knowledge is based on certain legal documents?)  - that what has been already taxed (in Spain) will be taxed again (in UK)?
What about double taxation convention between Spain and UK which is still valid?