The
Nightstar could have been the train the OP is imagining, but it's highly unlikely. As Failed Unit has said, the stock was sold to
VIA Rail Canada before it could enter service, for many many reasons.
1... the budget airlines suddenly came on the scene, offering unheard-of £50 returns to Europe. Suddenly travel to Europe was cheap.
2... the trains were designed to be upscale sleepers... many of the bedrooms were en-suite (and therefore the carriages needed very heavy water tanks) and the whole design was centred around a premium experience and therefore premium fare that would never have been competitive with the low-cost airlines
3... the Nightstar was a technical disaster. With the water tanks mentioned above, it would have had an axle weight too great for many UK railway lines, immediately putting the kaibosh on any plans for through services from the UK regions to continental Europe. Secondly, IIRC the whole rake of carriages would have drawn more current than could reasonably have been supplied by the overhead power (although I'll need a more technically minded forum member to explain this one). Basically the train would have needed two locomotives or even an additional generator van just to power it.
4... despite being based on the BR mk. 4 (?), the carriages were effectively a new design... they were untested and unproven. A huge start-up expense would have been involved in getting them into service.
All these discoveries were made at the same time. It was the perfect storm for the Nightstar. Through trains from London and other regional UK cities to European cities could have worked then and could work now, but the Nightstar was not the train for the job. It was over-specified and would never have been competitive. Perhaps now, with the possibility of competing services through the chunnel, SNCF, DB, Eurostar and others could possibly pave the way for high speed daytime services between the UK and continental Europe. But I suspect the precise safety specifications required by the Chunnel will prevent sleeper services from being viable for a while yet.