BOAC;
b) WX avoidance is not normally a MAJOR diversion and would almost certainly have been considered.
To put a bit of flesh to your comment, for an A330 on such a flight, a 30nm to 50nm lateral diversion (to the left or right of course, for others), around enroute weather would burn between 200 and 500kg of fuel. In effect, (it can be worked out mathematically, and some here have done so), such diversions add perhaps 40nm or about 5 minutes to the flight plan distance/time. The A330 burns about 100kg per minute in cruise.
The arrival fuel was, if I recall either from a comment here or from the BEA report, about 6.5T which is pretty standard for an A330. Even a major diversion costing 1000kg would not compromise arrival fuel seriously. Minimum fuel for the A330 (the point at which the "low fuel caution" comes on) is about 2.7T depending upon a/c pitch attitude.