I think it can 'win' on longer journeys, where an overnight stay on the train enables you to cover a far bigger distance than you might comfortably wish to do in a single day (while awake).
I think Brits would quite like a train that could go direct to Spain, for example, even if it just ran in the summer months.
You could then build modern stock to use as efficiently as possible throughout the year to selected destinations.
I am sure they could make money, especially if they adopted the idea I've said for ages (and may well be happening) where you have first class cabins, accompanied by airline style beds/pods for standard - thus allowing a lot more people to fit on a train.
We've had this discussion before, years ago, but the economics simply do not stack up. Let alone the politics.
London - Barcelona would be in the order of 8 hours non stop using the LGVs at full speed (if you could persuade the French to give up night time maintenance, which they won't).
But let's say you could, you wouldn't get much sleep on a train bowling along at 300kph, what with SNCFs rather liberal interpretation of cant deficiency. So they would have to go slower for comfort. And they would have to stop for crew changes. And there's unlikely to be enough traffic to fill a nightly sleeper to Barca non stop, so it would need to stop en route elsewhere, eg Lyon, Montpellier, Perpignan. You'd be looking at 12 hours minimum. By comparison the current sleepers from Paris to the Spanish Border at Port Bou take 10h30.
12 hours means 3 sets of drivers / guards (based at 3 locations) and 2 sets of on board staff. To provide the sort of service 'first class' passengers expect, would need 1 attendant per coach for first, and 1 per 2 coaches for standard. Say 8 per train. That's a total of 22 staff shifts per train, most of whom need paying at a rate for people willing to work permanent nights and being (at least) bilingual. Rule of thumb is that actual staff costs are broadly twice salary, so it's not unreasonable to say that just staffing one train will cost £10k a night. Many would be lodging at the end of journey being away from home, but that is small change in this.
Track access fees will be easily treble that per train. It's several thousand just for 31miles of the tunnel. Let's say £30k London to Barca predominantly on high speed lines.
Energy. These trains will need plenty just for hotel power. Plus the juice necessary to get the trains up to 100mph+ for the best part of 12 hours. Another £5k.
Carriage servicing / maintenance, being optimistic we will use existing facilities, but still need a few people at either end to remake beds, clean toilets etc etc in day time. Plus full maintenance over the year averaged (these will be high mileage trains). Another couple of thousand a night.
Cost of the train. It will be minimum £2m a coach. 12 coaches, plus 2 service vehicles per train plus a couple of spares. £30m+ Capital. Dry leasing a train will be c£3m a year. Call it £10k a night.
Loco hire (or power cars if we're doing an MU). A single loco to go all the way will be very complicated and rather specialised (particularly to meet SNCFs axle loading requirements on the LGVs). So power cars will be best. Whichever way you add it up it will be another £10k a night for one train.
Staff at the stations either end. Either your own or hired in from 'other' operators. Another couple of thousand a night.
Overhead costs of selling tickets, running website, renting space at stations, managing staff (over a very wide geography with various home bases), managing the contractual issues with at least 4 infrastructure operators, and generally running the company. Let's add 20%.
I make all that about £90k cost per train, and having worked in the sleeper team many years ago, I think that's being optimistic.
Let's say this train has 4 coaches first class at 8 cabins per coach, 8 coaches standard 'pods' / lie flat beds at 20 a coach, 192 people per train. Assume a (very) optimistic 85% occupancy (Cally Sleeper would kill for that). 165 punters per night.
That's an
average ticket price of £545 per one way trip to break even.
I genuinely don't know anyone who would be interested. Let alone several hundred a night.