Sleeper trains.
Most people in Britain have never been on one, especially in England. Why? Let us look at GWR's Night Riviera sleeper train, from Paddington to Penzance. The average cost per mile, for the train, based on the track milage, for a private room is £2.20. In Comparison to drive, a slightly longer distance is £0.14 per mile, over fifteen times more expensive! And this is on a Thursday in May! What is more is that the train leaves Paddington at quarter to midnight! A car journey, taking 5 hours rather than eight, can leave at any time you like!
That is what puts it out of the picture for most, apart from people who do not drive and tourists/ enthusiasts. Another factor is the UK's rail system. Our 'Loading gauge', the space between tracks is much smaller than every other country, meaning that are trains must be a lot thinner. This means that there is extremely limited space for 'bedrooms' and so therefore the are not many of them. Not many = high price.
The only other sleeper service in Britain is the Caledonian Sleeper, and it does not fare much better. Between London and inverness, it is an average of £1.70 per mile, again compared to the £0.14 of the car. However, the convenience is better here, with driving taking almost 10 hours, and with the train at just under twelve, with no effort/ concentration required, that makes it more attractive, but the cost is still something that instantly turns people away. If we look to America, their most expensive sleeper is at around £0.30 per mile. That is massively under the UK, and their cheapest is cheaper than driving, and comes with 3 nights accommodation, and meals!
In conclusion, In England sleeper trains are seen as a gimmick, fun once or twice, but too expensive to be a regular occurrence. Due to lack of space, it is difficult for them to be able to run these services and if the companies do not find a way to cut the costs, then they might not be around for long, so get out there!