I spoke to a very senior management pilot about this situation and he said that the CAA were aware of it and were happy with the way things were being done(commercial pressure?). Question is, how much margin for error is there in the performance manual when talking about weights. Things are fine when both engines keep going during the take - off but what happens when it goes quiet on one side just before V1, at max take off mass (as far as the loadsheet is concerned) when in actual fact, in a 200 seat aircraft we are 200 x 7kgs overweight. Now I am no engineer but the kinetic energy of 1.4tonnes travelling at 150kts, I assume, would convert into a fair deal of extra heat energy on brake application. Are the brakes up to the job? It would be interesting to get an engineers expert view on this matter or an expert in performance calculation.