The mailbag changed trains without stopping

Hornby-Dublo’s Travelling Post Office turned a passing train into a small mechanical performance. A mailbag waited on a trackside standard; another could be carried inside the Royal Mail van.

The 1962 catalogue explains the sequence. As the van approached, the operator held down a push button. One sharp knock marked the bag being thrown into the lineside collecting box. A second marked the waiting bag being caught by the net on the moving van.

The apparatus included its own short contact rail, and Hornby offered separate two-rail and three-rail versions: sets 2400 and 3400. That distinction matters if a van and an apparently matching lineside unit have been bought separately.

For anyone who ran one, how reliably could you exchange both bags at speed?