jcnorway
...Do BA allow the crew to take items from the bar trolley for own consumption?...
No.
BA has a specific
Crew Purchase Scheme which permits operating crew members to purchase small quantities of some beverages from the aircraft's bars - to be taken off the aircraft and for their own personal use - subject to certain restrictions.
The scheme requires that a receipt be issued, by the bar operator, for any beverages purchased.
The
good old days 
stopped long ago, during Sir Colin Marshall's time as CEO.
From your brief description however, the crew member may well have been in compliance with the scheme, despite how it may have appeared!
Breach of the scheme rules is now taken very seriously, with dismissal the normal sanction for any deliberate breach.
Best Regards
Bellerophon