Thanks for the answers, suggestions and conjecture.
BOAC .. CMR = 1800 and you say that commencing the approach with a predicted landing fuel of 1200 = problem? ie you have committed and have breached no legal limit.
I want to know what the perceived wisdom is concerning arrival fuel. Personally I feel planning to arrive with a CMR of Low Fuel with NO mitigating factors is not correct or commensurate with good airmanship.
That said if you are up against it (Low Fuel), due enroute problems, should you have a gear, flap, slat, hyd, cont, brake problem then you need to be absolutely clear about your rapid course of action!