The follow-on to that some years later, after massive overcrowding problems, was a bit of a rejig in joining the Birmingham to Scotland services to the Euston to Wolverhampton ones, having the effect of freeing up a unit by only having one VT service per hour between the two and having one rather than two layovers (though southbound they wait at Wolves for a while for a path). They also rejigged to run most of these services using double Voyagers or Pendolinos (though the quieter ones use single Voyagers), and to use single Voyagers on some of the quieter Euston to Brum services.
This was quite clever in that it didn't really annoy many people (there are loads of trains from Brum to Wolves not to mention a tram and half a million buses as well), allowed better use of capacity thus avoiding the serious overcrowding that was the case on Brum-Scotland services, allowed them to nick a bit of revenue off East Coast by running a direct two-hourly Euston to Edinburgh service, and allowed them to nick a bit of revenue off National Express by having direct Euston to Scotland hourly but slower than the "crack" Glasgow expresses, meaning the opportunity to price-differentiate by offering much lower Advance fares on those trains. Not to mention serving the ever-growing market for travel from Milton Keynes, who have the choice of the direct service or a connection using the Chester/Holyhead run about 25 minutes later; my observation is a reasonably even split between the two options.
All in all, it has been a very popular move and required no additional rolling stock at all unlike the other proposals for Birmingham-Scotland. Yes, the Voyagers run under the wires, but no more than they otherwise would have done, and the whole thing would work fine if you swapped them for some other kind of 125mph 5-car EMU just keeping enough for Chester/North Wales. (The added acceleration of an EMU would probably catch up any losses from lack of tilt).