TKR,
If you flew with BA long haul, it would have been on a 777 or 747. These aircraft do not have self-help exits (overwing or otherwise). That's why you didn't get a briefing. A crew member is allocated to sit at each door/exit and will open the door. Also, there are instructions on how to open the door during the safety demonstration as well as instructions on each door. In the case of a pre-planned emergency where evacuation might be needed, able-bodied passengers would be briefed on door operation and other instructions.
Hope this helps and clarifies
Gg