I did this as well - at first joining ones organised by the Warwickshire Railway Society and later on, with friends, by writing to the relevant Division. I didn't encounter the difficulties you mention, but then I never tried the Stoke Division - and it's odd that the D.M. Stoke at about that time was a well known railway author.
Fancifully, perhaps: one gathers that fifty-odd years ago, the highest echelons in B.R. took a rather dim view of railway-enthusiasm on the part of anyone on the management side of the organisation; might the D.M. -- for this reason, viewed with suspicion -- have been trying to offset that effect, by making a point of being harsh and unyielding about brake-van trips?
With it all being half a century ago, I've forgotten a lot of the details: I did BVTs in a variety of parts of the country; with most Divisions, as mentioned, officially allowing it -- but a few, including Stoke, not so. I remember difficulties involving the Holme -- Ramsey (North) branch, close to where I then lived: IIRC whichever Division that fell under, refused to cater to would-be brake-van-trippers. Thoughts were had, of going to the branch "on spec", and asking a favour of the staff on the spot; but never got round to actually trying that. Once I happened by chance to be at Ramsey (North) when a short freight train was just then leaving for Holme; but begging a ride on it was not at that juncture, possible in practical terms
I remember when I travelled Colwick to Burton ( on the mainly ex G.N. route and over the viaduct), on presenting myself I was told buy a ticket at Netherfield & Colwick station - which was of course technically invalid, being routed via the ex Midland.
It did seem that the Divisions felt some obligation to provide this facility - I was never challenged or asked why. The limit to my journeys was that an early start from a
distant location would often be involved.
In a previous thread, there was a bit of discussion of the above general "scene", largely concerning the distant past rather than our own late 60s / early 70s time of engaging in this stuff. The matter was raised there, of acceptance of would-be passengers -- including folk straightforwardly wishing to get from A to B for "sensible" purposes -- paying the normal standard fare, and travelling to their desired destination in the brake-van of a freight on a closed-to-passengers line: it would appear that it did indeed at least to some extent, happen -- well, as per your Netherfield & Colwick experience. I'm pretty sure that I and my fellow-brake-vanners never had occasion to do things this way; perhaps in part, a matter of attitude -- we (as well as the populace as a whole !) felt that we were engaged in trying to do something thoroughly weird -- accomplishable only by getting special permission from Authority if they would graciously grant it, or trying to make surreptitious on-the-spot arrangements if they wouldn't: it could be that this worked out for us as something of a self-fulfilling prophecy.
@Merle Haggard said: "Reception by guards ranged from indifference to friendliness; once, in South Wales, I was not only invited onto the loco ('Keep your head down going through Newport'), but, when returning from Ebbw Vale engine and brakevan, the driver stopping (on the running line) at a colliery so we could photo an interesting colliery loco."
I and my fellows in this business almost always found the train crews pleasant towards us -- polite even when not very interested; often, entering into the spirit of our doings -- I suppose it provided a welcome bit of variety and unusual-ness in their job. Invitations on to the loco came our way quite often; even, once or twice, with steam haulage.
