Originally Posted by Heathrow Tower

Quite. Well, of course the airlines would say they are campaigning to reduce their cost, not the service level, and thus efficiency will increase. 🤷‍♂️

Sadly, the airlines (in terms of corporate view, not that of the pilots) view ATC as a cost. Both en-route ATC (NERL) and airport ATC, regardless of provider, are both seen as a cost burden. UK CAA is under pressure (from airlines) to reduce en-route cost, just as airports are under pressure (from airlines) to reduce airport ATC costs. Large airport ATC units can most certainly have standby shifts, increasing resilience, but that would require increasing the number of controllers (and hence cost) by 30% or something, which is not something the airlines will permit.