Under its targets, the Border Force must get non-EU passport holders through immigration at Heathrow in less than 45 minutes for 95% of the time.
Its target for EU passport holders at Heathrow is less than 25 minutes for 95% of the time.
When you've travelled from, say, Paris, the time in the air is likely to be little more than the target time quoted above for non-EU passport holders. Who thinks such loose targets are acceptable? In many hundreds of business flights, it was almost always my experience as a returning UK citizen that border formalities would take minimal time. That's how it should be. In my view, 95% targets of ten minutes for UK/EU citizens and 30 minutes for non-EU citizens would seem to offer reasonable service. That would give median waiting times nearer 5 and 15 minutes respectively.
There's no reason at all why the Border Force can't know at any time of any day exactly what volume of passengers is due to enter the country at any time in the next two hours, and to a high degree of accuracy also in the next day, week and month. Once passengers are on their inbound plane and the plane is in the air, the border staff should be rostered to meet them. It's not rocket science.