Zem old zyztems is always the best. Lyke a real person selling tickets ...
Now if the Thingley South to West curve and Bradford East to North curves were still in place, the line would be fantastically more useful for diversions such as this one. It takes 10 minutes to get a train from Thingley Junction up to Chippenham, reverse it, and get it back clear of the junction and they were having to do that "dance" between 2 x 125 ah hour each way.
Similarly, those links would mean that Chippenham and Bath wouldn't have to be missed out of all the London - Bristol services if there was engineering works in the Corsham and Box area.