MarkyT Yes I think you are right about that. Yesterday, arriving at T.M. I walked through the side entrance (in many ways now perhaps the main entrance*) and pondered the fate of the lone figure at 0300, say, in that huge nearly empty building, when all that is to be controlled is a straight line between south of Parsons St and south of Bridgwater. One wonders whether the stretch could just be 'switched out' in the night hours.
*It would be interesting to monitor the footfall. Of course, once the platforms in the Digby Watt / Brunel building are reinstated, it won't be so handy, as one will have to walk under a rebuilt subway, which, IIRC, was halfway down the 'Midland' platform.
Edit: Having looked up a few details, it seems that Sir Francis Fox was the architect responsible for the extension of the Brunel building in 1878, when some of it was replaced. I've got a book so will look into that further. The building is in three distinct sections, the most southerly is the Brunel GWR Head Offices, then the 'Passenger Shed' which is of the same design, but has a wider overall roof, then the brick built extension, which is what I always knew as the 'Midland side'.