BA:
747 - Cabin Crew rest above cabin.
777 - 200 - Cabin Crew rest above cabin (where fitted) or High Comfort jump seat.
777 - 300 - Cabin Crew rest above cabin.
767 (Long Haul) - last row of economy seats (3 seats)
767 (Short Haul) - no.
Airbus - no.
Short Haul 767 and Airbus crew also operate just under 12 hour duties, but the "rest" is taken on the ground during turnaround whilst dodging the cleaners and caterers, security checking the cabin and boarding the next set of passengers.
Sometimes, depending on load and with permission from the captain, we are permitted to sit in the back row of the aircraft if there is time, usually just on things like the night DME and SOF services. Although the night SOF which operates in the summer schedule has a turnaround of 2H55 in SOF and most crew take pj's and sleep for an hour or so on the ground.