I'm an offshore worker working in the brazil basin or gulf of mexico america doing month on month off for a british company.im now full time resident in spain since beginning of January but still paying british tax. Do I pay british tax or spanish tax. My company advised I pay british tax while I live in spain.why?

Because you are working for a british company. That's why you pay british tax, and not spanish.

im an offshore worker working in the brazil basin or gulf of mexico america doing month on month off for a british company. im now full time resident in spain since beginning of january but still paying british tax. do i pay british tax or spanish tax. my company advised i pay british tax while i live in spain.why?

This forum is for U.S. taxes. If you are a U.S. citizen or resident, then you must report the income on your U.S. tax return.

Tickle is not quite correct. You have not been resident in Spain long enough to fall under their taxing powers.
It is your residency, not who is paying you, that determines who gets to tax you. The other country will give a tax credit to avoid double taxation.