The original business case was for 18tph, which HS2 now say probably won't run. It is now likely to be 14tph. Read the link I posted- especially Lord Berkeley's letter. Or don't.
Funny how you were criticising me for saying the benefits were "might" and "could", and now you're saying we can't say for certain until everything is finalised. Make your mind up!
No, what I'm saying is that until we know what services those 14tph run we don't know if there's going to be a reduction in the frequency of services to individual stations.
Without knowing that we can't be sure that the drop in services are going to have the impact which is being suggested.
I've already highlighted how Manchester could see a lowering of capacity which is unlikely to have a significant impact on the capacity. However by making that change it could allow another destination to have a service.
Likewise 1tph could run London, Birmingham Curzon Street and then onto Scotland (much as 1 of the 2 services to Scotland goes via New Street). Scotland would still have the ability to have 2tph from London (1 would be longer than the other but still a faster than the current fast service) but you could have that second service use the path of one of the 3 Birmingham services. If you say ticket prices a bit lower on the longer service then you could still carry as many passengers, the ticket income might be down a bit but probably not but much. You'd also save the cost of having to run a whole extra service from Birmingham to head to Scotland.
This would either reduce your costs of running the services. This then benefits your business case.
As such the loss could be fairly small, or at least smaller than would be implied by the loss of those 4 London services. As rather than it being a do from 18 to 14 is actually a drop from 24 services (18 to/from London plus 6 to/from Birmingham) to 20 services which is a 16.6% drop in the number of services. However even that's simplistic as it could be that it allows more Birmingham to elsewhere services to be run. This could have an impact, but it's only the delay of going into and back out again of Curzon Street and not the loss of the whole service.