I remember once travelling on the sleeper from Edinburgh to London overnight on 23rd/24th December.
As there were no return services on 24th/25th December, there was a crew change at Preston, with the Scottish crew working the train between Edinburgh and Preston, and the London crew between Preston and London.
When I used to work at Euston and Kings Cross, I would regularly see sleeper staff coming into and out of the various hotels in the area.
I have also seen Eurostar staff use the Premier Inn in York Way, Kings Cross.