shoot the mesenger!
The messenger was right though. There
are crossing traffic flows, but you'll find no crossing upper air routes at MARGO getting in the way, which is what you inferred.
Most domestic traffic will be ABOVE the North Atlantic traffic coming up with them through MARGO so a restriction to solve that problem would look nothing like the MARGO restriction. It would be more like Max cruising level FL240 for traffic landing in the Scottish TMA, hence removing the confliction you suggest.
I quite often remove the MARGO restriction when I can, and see aircraft crossing MARGO even lower than FL260 when given unrestricted descent. Can't be that bad then can it ?
Rolaand is right. Taking traffic out of a sector which doesn't need to work it, by imposing a level restriction, frees up capacity for those who have a much greater need to use it. Volumes of airspace have a defined capacity, above which some form of regulation is required to ensure that the overall safety of the system can be managed, plus some contingency built in for unusual circumstances. Imagine sitting on the ground with a 2 hour delay to fly up over MARGO and onwards across the Atlantic, just so that some domestic traffic can get their best possible profile. Or be sitting out your delay on the ground as a UK domestic aircraft because some Johnny Foreigner has already been airborne for 3 hours and has filled up a slot through MARGO which lets him be a couple of thousand feet above the current profile.
NATS do work with the operators (note, those who make the decisions, not individual pilots who will have wide and varied views) to see what they want. Where you can't have everything, then a choice has to be made. The current choice is capacity.
I wish I could see how many planes there are going over the pond that actually need to be so low over MARGO that every plane going in to the TMA has to be thousands of feet below their optimum descent profile (esp if there is a north wind) and burning fuel that the airlines cannot afford, also how busy does a controller have to be that the coordination cannot be done. Redesign the sectors if needs be .
Alternatively, redisgn the airline schedules so that 10 aircraft are not trying to use the runway at the exact same time, 10 aircraft are not trying to fly the same route at the exact same time, 10 aircraft don't want the same level at the same place at the same time. You could call it Free Flight !