Here are a few reservations that I have about the current HS2 plans. Where shall I get started?
The idea of having separate branches for Manchester and Glasgow rather than a through line connecting them both is just absurd. Why would you just want to allow travellers from London to reach these two cities, and not link them with each other? The idea of putting as many cities as possibly on their own deprecate branch lines has got to be a joke, given that the very purpose of any line is to link places together, not to drive them apart from each other up different branches.
OK, lets assume for argument's sake that the HS2 Main Line is London to somewhere around Preston via Birmingham and Manchester City Centres.
To meet demand (and ignoring other possible destinations for a second), you *still *need 8 trains per hour south of Birmingham to meet the combined demand of Glasgow (2tph), Manchester (3tph) and Birmingham (3tph) to London, which *is* where the demand is, whether you like it or not.
So you're sending all passengers from Glasgow on a detour without really saving any operational cost (and probably increasing it slightly in fact) to justify it, whilst also making the operation of the Birmingham and Manchester city centre stations more complex with trains that are not providing useful capacity there (being in excess of requirements)
And all this is before you've considered the complexity of engineering cross-city high speed infrastructure for these cities!