A few points;
The 'Cobbler' train was the result of an initiative by the newly-formed Northampton Development Corporation, the leader of which invited the Chairman of the B.R.B. to visit Northampton. Presumably the latter travelled by train, on the hourly service calling all stations in a 4 car 75 m.p.h. e.m.u. with draughty doors to almost every seating bay, which might have helped the argument. The Chairman agreed to a single fast service in each direction. The railway then was, of course, operations-led and it may possibly have been the case that the operators did not like being told what to do, not even by the Chairman, but they certainly took time and kept finding problems. It was claimed that there were no paths to cross fast line at the then-new Hanslope high speed crossover, so it crossed out at Bletchley initially - which gave rise to the Bletchley call, because the crossing was 20 m.p.h., so you might as well stop. Similarly, there was said to be a shortage of locos., so it was diagrammed for Cl82/3/4 - there was no spare in even the cl81/5 diagrams, allegedly! It started with the winter 1974 T.T., from memory. The stock was Mk1s and this was their only work of the day, spending the day in the sun on the bank outside Euston.
It was around BSK+CH+10xTSO and when it became full, there was pressure to have a second service, and eventually it reached 4. As it happened the Divisional Passenger Manager at the time lived at Leighton Buzzard, and he agreed to introduce one of services on the condition it called there so he could travel non stop to work. Such was the basis of decisions in those days.
The Airbraked train was an Oxley E-B-W Inter-City set that was otherwise running e.c.s. to Euston for the down morning peak and similarly in the evening- the decedent of this was the double Voyager e.c.s. from Central Rivers depot to Euston to form a down Holyhead that provided a morning up service from Northampton until the covid changes.
When the last train was introduced it was clear that difficulty in finding surplus Mk1s was being encountered. It, at one stage, included veteran SK 24006 and a few 48 seat SOs and an FO marked 'Motor-rail trains only'; some coaches were not actually branded '100m.p.h' but I'm sure that was fine...
The coaches in the Mk1 sets, all the way from 1974 to the demise in 1989, remained the same, and interestingly many of them are still around either on.heritage railways or charter trains. Mostly, they were the later ones with Formica panelling and aluminium window frames, and I remember 4936/84/94 and 4997- 5002* particularly. Right at the end, they got the NSE refurb of new lighting grey panelling and N.S.E. moquette.
Changing the subject, shoe traffic was lost to road in the 1960s, the last Northamptonshire rail traffic being from Rushden. There was a number of local carriers who specialised in the traffic, Townsends and Wilkinsons being the two I remember. However, it was costly traffic to carry because of the way the shoe industry worked. Each evening, shoe shops would place an order with the shoemakers (and there were many - even in the 1960s) to replace the shoes that had sold that day e.g. ;'one 7 1/2 brown men's brogue, one 9 black men's Oxford' - penny numbers. And the factory then made up the order, and sent it off. So very large numbers of small parcels to everywhere in G.B.
* the Cobbler sets were used on football specials at the weekends. On one occasion I recollect boarding the train and deeply etched by knife into the wood veneer of the vestibule, in enormous letters, was 'Q.P.R. = ' and then a very rude word. A couple of years ago, I similarly boarded a Mk 1 on the Great Central and that wording could just about be made out under thick new varnish.