I travel by train regularly in the UK and it isn't unusual to take up to 8 hours to get anywhere :)
The closest I've been to a sleeper in recent decades has been five hours on a cold station because cancellations & delays have meant missing the last onward connection of the day so waiting for the first morning service (there are supposed to be provisions for that by way of providing accommodation or replacement taxi service, which do sometimes work, but at that time of night there isn't always someone available & reachable to enact such policies).
I’ve had my fair share of poor UK rail experiences, especially during holiday periods. Standing on the train from London Paddington most of the way towards Exeter is never fun.
In the case you couldn’t reach someone, doesn’t every platform have a phone as well?
The closest I've been to a sleeper in recent decades has been five hours on a cold station because cancellations & delays have meant missing the last onward connection of the day so waiting for the first morning service (there are supposed to be provisions for that by way of providing accommodation or replacement taxi service, which do sometimes work, but at that time of night there isn't always someone available & reachable to enact such policies).