I won a £5,000 Premium Bond prize

I didn't think you could be taxed on your winnings? If you won it in pounds why would Spain tax you?

I think I might have spent it before income declaration time 😊

Steve 

Leave  Cash in English  Bank account  if you have  one. 

If you win a prize on the Spanish lotteries you have to declare it on a form 136. There was also a change to the rules a while back and the first €40,000 of winnings is exempt from tax and then 20% of winnings above that.

I don't know if this applies to foreign winnings but I'm sure a gestor would be able to tell you.

Because as I am resident in Spain for tax purposes I must declare my worldwide income to the Spanish tax authority irrespective of the the currency and country in which it is received.

Yes but winnings aren't classed as income. And as marcliff said, upto 40k you're ok

"what rate of exchange I should use for non-euro income"

For all declarable income the rate is what it was on the day you received the money, it's as simple as that!

You may find the contents of these links helpful:

https://www.blevinsfranks.com/how-uk-investments-are-taxed-in-spain/

https://www.blacktowerfm.com/news/do-you-live-in-spain-and-still-have-uk-and-offshore-investments/#:~:text=In%20the%20UK%2C%20you%20don,are%20taxed%20as%20general%20income.

Thank you for your reply. I had in fact found the Blevins Frank's advice online last night, which is confirmed in your link to Black Tower. 

With my marginal tax rate of 37% this means that the Spanish tax agency will be helping themselves to £1,850 share of my £5,000 winnings when I make my declaration next year -  unless I can claim that I have not yet received received the winnings because in my case any winnings are automatically reinvested in new bonds. It would be interesting to hear members' advice on this possibility.