I guess that's one way to handle it, but does rely on the TM being available and a revenue block being possible (or requred...)
I was more thinking along the lines of the below. And this is from someone with no operational knowledge of Euston, just lots of painful usage:
- ex Manchester arrives at 0941 and will form the 1030
- Passengers are off by 0946
- TM clears train and locks it at around 0946 but lets call it 0950
- Cleaners use carriage key to open whatever door they fancy (C and K crew door usually for restock)
- Simultenously with the above, or when the cleaners give the signal they are onboard, the train appears on displays as "1030 to Glasgow - Wait on platform 1"
- Cleaners finish cleaning at 1000 and lock doors they were using
- TM, driver and crew turn up at 1005 and once happy for boarding to commence, unlock the train for passengers. Platform displays change to "1030 to Glasgow - Boarding Platform 1"
- Ramp doors close at 1028 and the train departs at 1030
- TM walks through train to do a ticket check before first stop
Timings will obviously be a bit different in reality, but you have passengers able to get themselves in position at doors 10 minutes after the service gets in and 10-25 minutes before the train would normally be called. If a train comes in late, then you get the benefit of not needing to split a revenue team to cover the late call and can get passengers off the concourse and ready to board as soon as the train and crew are ready. And if you regularly have passengers waiting on platforms, that could open up extra retail opportunities on the platforms themselves. Plenty of space for a small coffee stand on nearly every platform.
Disruption and overcrowding could be relieved by shifting passengers down to the platform ramp that their train is expected to go from, leaving the center of the ramp open for passengers disembarking. Or even onto the larger platforms as they have plenty of space to handle waiting passengers and people disembarking. But the more you do the sensible option and keep people informed and near to a train, the less passengers feel like they have 30 seconds before their train will leave so they'll rush less as a result (that'll take lots of time).
Yes, last minute changes or crew issues would result in people having to move to another platform, but once you have the main concourse quiet and no scrums beelining for a platform you improve circulation. And there is even the parcel ramp that could be converted for passenger use if NR really gave two hoots.