BOAC, I really doubt there was a clearance to descend to 50m. If there were one, it would've been registered on the CVR track that was written directly from the radio, and it hardly could have been unintelligible. Besides, it doesn't correspond to any procedures either on the field charts or even in the Tupolev manual. So until/unless we have a confirmation of such a clearance from the MAK, we can safely dismiss it as an unsubstantiated rumor.