Did make me wonder if ego got in the way of sensible decision making.... WHY send a plane to Scotland with 26 onboard only to have it fly back with just 6? I'd understand if the return was packed; but why not just leave the pulled flights cancelled?
LHR operates a use it or lose it policy wrt slots.
This would apply to days with no industrial disruption. I am sure that we have dispensation to cancel with industrial or WX disruption.