What cc of motorcycle can i ride in spain on a british car licence?

i am a resident off spain with a full british european style licence,and i want to buy a motor scooter,but have not passed a test on a motor cycle

If you are a resident of Spain, you can't drive with a British license. You need to swap over to a Spanish license anyway. If you ever get stopped by police, they will require a Spanish license, especially if the vehicle belongs to you. If not, they can fine you. Once you have a Spanish driver's license, you can use up to 125cc or 15 horsepower without a seperate license or test as long as you have had your driver's license for more than 3 years.

50cc

Providing you have held the full car licence for 3 years then you can ride up to a 125cc motor cycle or scooter, without having to take any sort of test.

I would guess 50cc, but it depends when you passed your UK licence