The Times published an Archive photo of a still-recognisable (to the habituee) "motor-omnibus yard" of Victoria Station taken in 1927 to mark the construction of the new control tower
So that's where they got the idea for guarding PoW camps from
The most surprising bit is that the route numbers stay the same despite all the changes. I would bet that they were even the same back in the days of the horse-drawn omnibus
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