That's very interesting, thanks, Mark. 

At the date of the film (1988), Bradford South Junction was still a double junction, semaphore signalled but with colour lights covered up and ready for use.   At Bradford East Junction, the two tracks from Trowbridge and the one from Bradford West (Bradford North Curve) all came together into a single line onwards via the site of Staverton Halt towards Melksham.

Had Bradford North Curve remained after the changes that were underway, we might very much have a different service pattern today, but at the moment priority must be (on passenger services) to broaden up the existing one from Swindon to Westbury to hourly rather than look at adding another thin one Swindon to Bristol via Melksham and Bradford-on-Avon.  Double track reinstated from Bradford South Junction to Bradford East Junction (circa 500 metres) or perhaps through Staverton (sadly, platforms there are beyond easy re-opening) would add a useful robustness for a train coming up from Westbury to wait for the single line clear of the main Westbury to Bath and Bristol line, or for a freight coming down from Swindon to wait for a slot between passenger trains without blocking a train on its way up to Swindon.

At the other end, Thingley Junction is already single, minimal, colour light, with the up train joining the down line for some distance before crossing over.

I did note a single line token picked up at Bradford East and remaining in the cab all the way to Chippenham Station (a gap in the recording had it disappear there by magic in one frame).  Which means that the effective single line section was all the way into Chippenham Station.  So that has improved somewhat in that a train headed down to Westbury can at least wait just to the east of Thingley East junction now, and if it's a none-stop train and the lines are clear does not need to slow / stop at Chippenham Station too.