In British English, behaviour is spelled this way - with '-i-', '-o-' and '-u-' together in the last syllable. (According to the spelling rules of American English, the US spelling omits the '-u-'. giving behavior. To use this spelling in British Higher (or any) Education risks condemnation.)
This is one of the 117 mis-spellings listed as 'Common difficulties' in the section on 'Spelling' within 'Writing' in UEfAP.