wondering whether BA are stirct on ATPL exam marks and if they ask to see your grades during interview or if you have to declare them
No, if you have previous airline experience and are applying under Direct Entry, its an online tick in a box confirming you have a full or frozen ATPL. If seeking employment with a fresh licence, your flying school will assess your grades for recommendation and to be put forward (first time pass in all subjects, average above 90%?)
I've had 11 pilot interviews over the years including two for BA and was never asked about exam results.