Sorry to not have a pic of that railway but the interior does looks sad.

Details extracted from a couple of souvenir books:
Westminster Abbey was handed over by the Dean to the Earl Marshal (Duke of Norfolk) for several months, for the Ministry of Works to prepare it. All monuments and memorial tablets were covered wih felt and boarded up before seating for 7,600 seats was installed.
Over two thousand two hundred square yards of carpet were laid in the Abbey and the Annexe.

To help move in all the steel and timbers needed for the seating a narrow-gauge railway was laid down the centre of the Abbey.
What a hoot! This system was first used in 1937.