I don't think in those times that routing from the through platforms at Oxford Road/Piccadilly right across to the Sheffield line was looked on with favour. One side was 25kV and the other was DC, and although there was pointwork going right across I don't ever recall it being used as such. Possibly the south side line was still used by the Harwich boat train, from Guide Bridge to Central, and then on to Liverpool Central, which was changed to terminate at Piccadilly some time around this. Early December would have been getting dark shortly after 3 pm, which really restricted the scope for railtours in wintertime in those years.
Office staff at BR offices also worked on Saturday mornings in this era. Another alternative on Saturday afternoons was to go on to the football, where games invariably started at 3pm, spending the intervening time with a group in a pub. These latter generally did not do food in those times, so it was common to have brought in sandwiches from home, which I presume applied to the railtour as well. It's notable in old photos of such how many are formally attired in ties and jackets, but this was commonly because they needed to come straight from the office.