I was an S&T Tech at Slough during the '70's. The Royal Train would occasionally arrive or depart Slough, using Platform 5, which allowed quick access to/from the Royal Limo to whisk her off to/drop her from Windsor. (Platform 5 was the rear access to Slough and the Platform and Road was easy to secure). We would be advised by our supervisor when we signed on duty that the Royal Train was due to arrive/depart (time given) and that we were to remain at Slough PSB during the time that the Royal Train was within Slough PSB sphere of control, (except when ECS once the Queen had departed the Train, but not when it ran ECS to pick her up).
The PSB Signalmen would also be told when they booked on, and there would always be a Divisional Manager in the box to oversee that all protocols were followed. The Train would operate in a modified block working scenario. The signalman would replace each controlled signal passed back to Red until the Train had cleared the overlap of the next controlled signal. The Signalman would then be allowed to clear the previous signal, by setting the route up to the next controlled signal. This was especially relevant at Slough, as many of the Signals between the boundary between Reading/Slough PSB and Maidenhead had many Automatic Signals. The protocol was that the Reading Signalman would replace his last controlled signal to Red at Ruscombe after the passage of the Royal Train, and was not to set up the Route to the PSB's boundary until the Royal Train had passed Slough PSB first controlled signal's overlap, that the Signalman Block Belled "Train Out Of Section" (2-1). (There were Buttons in the Panel to allow Block working in emergencies). Also the Signalman at Slough would phone the Reading Signalman to confirm the above had been carried out before the Reading Signalman set up the route for the next Train.
Didn't always work. One Reading Signalman allowed the Reading to Paddington Stopper straight up behind the Royal Train one night. Suffice to say that the Divisional Manager in Slough PSB was not impressed and a 'Number One' was duly issued to the hapless Signaller.
