Andy R. A. Thank you for the response to my post (I didn't 'quote' it). There were errors in my post, but the purpose of these threads, in my opinion, is to trigger responses from people who know can add recollections.
My errors were due to the passage of time. My contribution was based on working in the London Division in the very early 1970s, the particularly relevant part being with the job title 'freight current performance clerk, Midland lines' (i.e. Sharnbrook Southwards). The current performance clerk kept traffic moving in the window between STP Crewe (more than 2 days notice) and Control (on the moment). I also worked in the Accident Section (injuries resulting from train movement) and FRS distribution (i.e. before TOPS), so, despite being harangued on other threads for talking rubbish, I did have some first hand experience - though, in the subsequent 48 years, I have had other stuff to remember, too, pushing that period to the further depths.
I now recall that the my emphasis on Acton traffic was not because it was the only traffic but because keeping Wellingboro' yard clear was one of the banes of life and woe betide me if any of my specials knocked a passenger service (Sunday specials usually did, because only one s/b line was usually available due to engineering work, and our finest locos struggled with 60-on of wet coal over the passenger line, if that was the only one open.
I now recall there was still traffic via Brent Midland. Another source of stress were the Northfleet & Southfleet coal trains. One terminal had bottom discharge (i.e. hoppers - flats had to be manually emptied) and the other had tippler discharge (i.e., flats, but hoppers could be tippled but sometimes their doors fell in with the coal). The Northfleet flow (which I think was the hopper one) ran through from Welbeck although sometimes got staged at Brent, but the flat traffic was aggregated at Brent from a number of collieries, so definitely Brent was still used for marshalling. The reason for my stress was (i) according to the terminals I was personally responsible for NCB loading their traffic in the wrong type of wagons and (ii) my wonderful colleagues at Cricklewood confusing 'Northfleet' and ' Southfleet' and going to the wrong place - 'well it's all coal, unit!' .
I'm not sure how the Welbecks got South but I'm fairly sure that most freight went Wigston-Glendon rather than via Manton then - passenger traffic was more sparse then. Certainly I remember a pile up on that route when D5383 was over-powered.
It was definitely the intention to divert via M. Harbro - Northampton rather than Wigston - Nuneaton; freight had already been diverted that way, and Midland pass. drivers had the route - in the event of problems to the South of MH., Class 1s were routinely diverted that way.
With regard to another post about St. P. - why was it the home of S&ISD?. Without blowing my anonymity, I hope, I later worked on the freight train ferry business management section after it passed back to BR and I can say that the accommodation for the international departments was always allocated to the less attractive outposts and buildings - for instance, in the garret rooms (former hotel staff quarters) of '222' or an office 20 miles away from 'civilisation'.
I hope that my recollections of 50-ish years ago are worth recounting.