Following the departure of the hospital, the only access to the roof space or attic of the church was through an opening in the north wall of the first floor chamber of the tower. This opening was about 20 metres above the floor level of the chamber which further served to aid the concealment of the old operating theatre. The opening could be reached only by means of a ladder and, after some difficulty and discomfort, any visitor would climb into a completely dark attic. The glass in the old skylight above the theatre had been replaced by slates and the dormer windows in the rest of the roof-space were black with a century of dirt. In addition, the attic was thickly covered with dust and some floor boards had been removed which made access even more hazardous.

In 1956, Raymond Russell was researching the history of St Thomas’s Hospital and decided to investigate the opening into the attic. Part of the operating theatre had been removed at some time, including all the standings, but most of the shell had survived. The passageway to the staircase, which led to the standings, was intact, and also one whole side of the staircase but not the treads. All the plaster work of the walls and ceiling was untouched, as was the greater part of the flooring. Inspection revealed that a false floor had been laid on to the true floor and that the space, of around 7 cms, had been packed with sawdust.

It is probable that the theatre was partly destroyed when wiring for electric light was installed in the new Chapter House, some 50 years earlier. The floorboards had needed to be exposed and most of the standings were in the way; the disturbed floorboards could still be seen where access had been obtained to the space above the ceiling of the church to lay the wires. A rather freer clearance was made than was necessary for installing the wiring and this may have been due to the presence of dry rot. This appears to be the only explanation for the tearing away of the panelling of match-boarding on the west wall of the theatre. Fortunately, the untouched ceiling plaster showed the exact upper limit of this match-boarding and, on the bare bricks of the wall, could be seen the fixing details of the vertical boards and their dimensions. Similarly, many details of the construction and method of fixing the standings were also visible. The semicircular shape of the theatre remained, even though studs that supported the south side had been sawn away.