Relative size of markets I agree on but not so sure about the lack of demand. The Bristol and Glasgow red eye flights are normally packed (can't speak to Edinburgh) - so there is a significant market there. Also, if you are assessing usage against current rail travel, then I would say it is being suppressed by the services offered for such travel, namely those awful CrossCountry Voyagers. Personally I never buy a Bristol to Glasgow ticket because I would be expected to use CrossCountry. Far better to buy a ticket to Paddington and then Euston to Glasgow. In all, it is probably not possible to fully assess the usage of a new sleeper service until it went live. And unfortunately it won't happen due to lack of rolling stock and will.