The cruising level has nothing to do with this, it quite legal to plan to arrive overhead manchester with fuel for the approach, 30 minutes holding and then divert to the 2nd runway, using the Jeppesen flight planning system and our B744 fuel biases, the required fuel comes to 5500 kgs.
I dont know the weight of the BA aircraft, so its quite conceivable that it planned to arrive with 5000 kgs. If you have problems with this, they shouldnt be addressed to BA but the JAA.
Mutt.