Waxy unfortunately your rock and hard place here . Your prospective employer would normally apply to the Criminal records Bureau . The information they give is based on that which is on the Police National Computer . Cautions are not held on that database. However for certain occupations they can apply for an enhanced check . This is then sent to the relevant force areas in which you have lived , hence the give us your last 10 years worth of addresses on your application form . This check would reveal a caution , this is primarily used for occupations like schoolteachers things to do with kids etc etc however at the moment since 9/11 it is more than likely that an enhanced check will be carried out by an airline but again it is down to each individual airline .
At the end of the day you are best disclosing it to them as some employers will take you on and send off for the checks after youve been employed , results take weeks and the last thing you would want is to be finishing the ground side of your TR only to be hauled into the chiefs office to be dismissed on grounds of dishonesty and integrity (got you by the balls on that one ) this would then be stapled to every job application and cv you send to airlines.
In my experience provided its not an honestly drink driving or perverted caution you should be ok but then how many other applications will be clean ones? that may be a consideration . But no it does not count as a conviction