BA @ LHR
A319 - 4-6 CC (max 132 pax)
A320 - 4-6 CC (max 156 pax)
A321 - 5-7 CC (max 188 pax)
B757 - 5-7 CC (max 186 pax)
B767 - 8-10 CC (max 247 pax)
Crewing levels vary due to sector length, overall loads & business/economy class split.
EG A MAN-LHR with a full load will generate 6 crew in the cabin on a 319/320, wheras a LHR - LCA with a handful of business will only get 8 crew on a 767.