Clive D. W. Feather wrote:
In article .com,
Stephen Furley writes
There was also another passage leaing off to the East, still in use by
staff, I think this may have led to the depot.

I think it did.

In the 1970s I went on a school trip that included Stratford Depot. My
memory is that we followed a subway from the main station.

The main entrance to the depot subway was on the front of the building,
to the right of the passenger entrance. Between the two was the BTP
office (though it didn't seem to deter many trainspotters from making
their way down the tunnel).