411A
That doesn`t sound too smart, now does it?
If you are down to altn fuel and you divert from LHR to, say EGSS, you would end up being committed to that field. Where there`s only one runway, nobody`s expecting you, you`re not familiar with the field etc etc.
My company does allow to commit to destination, as long as you land with at least 45 min fuel. The considerations to take into account when coming to this decision are left to the commander.
How about that for common sense eh?