GRUNT was referring to an en-route scenario. We have to stay within 5 miles of the centreline of an airway or upper air route to ensure protection from other traffic.....if we vector or clear traffic off route we have to co-ordinate with the military and other agencies. UK traffic is dense and we do not have the luxury of one-way routes except in a few areas, where special conditions apply. If you run 2 or 3 abreast in the same direction...or have opposite direction traffic.....a modest 5 degree heading change will suffice for high level and high speed traffic. Any more might require constant correction to remain inside regulated airspace. A 5 degree change will move an aircraft's track 5 miles per 60 miles travelled. In the case of aircraft on parallel tracks it may be necessary to make a minor heading adjustment to ensure 5 mile minimum spacing.....if it drops to 4 miles we get an "instant-day-off" voucher from the supervisor, because the big red light on his desk has just lit up.
Some of the cobweb of routes available to UK civil controllers changes regularly, particularly the range of part-time or "conditional" routes. Many of these are controlled by military needs..........and besides these, there is a network of corridors and reserved military airspace and danger/restricted areas that can be actioned at 5 minutes notice in some cases.
We don't get paid per heading.....we get paid to provide a safe and expeditious service. The argument of quantity or quality is a fine balance....if you reduce my traffic I may not need to assign headings. If the sector traffic throughput is flow-controlled at 30 per cent above design load.....expect headings.