Eye in the sky is correct -
Yes JD - the TL is easy to calculate - any ATCO or Pilot that can't needs shot
- however Mcdhu states they were flying into LGW... they (LGW) may have had had traffic descending and passing 6000' - telling McDhu to descend to 7000' Alt knowing full well that at some point in the very near future Mchdu would have been descending further - on the QNH - is emminently sensible.
Unfortunately we can only speculate as to the situation at the time.
As for low pressure and FL70 not existing, EyeInTheSky is again perfectly correct - FL70 is not seperated from 6000' departure from EGLL, but is is seperated from FL80 etc and it is perfectly acceptable and sensible practice to use it on low pressure days- provided that when using it you are aware of what is is and is not seperated from!
Those people that cannot work out TL in their head would probably be best just to plod along and stick to the silly notion that it isn't available though!