Firtst up, HS2 not stopping until Birmingham is not an issue. This is because the WCML already has a finite number of stops between London and Birmingham, therefore to provide a faster version (which is the point - to get IC travellers of the exisiting network, so that there is more spaces for passengers from those stations without a HS service) it would need to stop at fewer places.
In the same way Motorways (and a lot of trunk roads which do a similar job) do stop at a lot less places than most other roads. For instance I could (if I so wished) drive 1m on a lot of roads before stopping again, even on some trunk roads there can be places where there is direct access to properties which can be easily be closer than 100m. Therefore to have a motorway juntion spaced only 1 mile away from the next (which is now the current guidance - however I am aware that there are several, but in the greater scheme of things very few, which are less than this) is massive increase in the distance between access points.
Even increasing the distance from 100m to 2km (single lane trunk road to Motorway) is 20 times the distance, therefore the station distances being replaces could go from 5 miles to 100 miles to have the same ratio of increase in access points.
I never understand this debate about load factors - HS2 is projected to open in 2026 - given Thameslink 2000 is expected to open around 2018 and Crossrail also in 2018 (when some hoped it might open in time for the Olympics) - I would put money on it not opening till mid 2030s to Brum and mid 2040s to Manchester and Leeds. So present load factors are irrelevant its what will they be in 20-30 years time that is relevant.
Full details of WCML load factors can be found here
https://www.gov.uk/government/publications/west-coast-main-line-demand-and-capacity-on-weekdays - and are a bit higher than quoted above
Form the link the passenger numbers on long distance (throughout the day) in 2010 are about 27,100 each way whilst in 2012 they are about 31,000 each way. Over two years that is an increase (using the arrivals as the difference is slightly lower) of 12.58%, which is a little more than 6% growth per year (which would be 12.36%).
If we see growth continue at 6% then it would only need to last until 2017 and 2020 before the predictied passenger numbers would hit the 2026 and 2033 HS2 opening years passenger numbers assumed in the model. Therefore there is a risk that with just 5 more years of growth (beyond the data that this report provides) we could see the WCML coping with more long distance passengers than there should have been when phase 1 of HS2 opens.
This could mean that rather than about 27,100 passengers (2010) it could be 40,650 passengers (2017) and 48,509 passengers (2020). Given that the capacity of all the services is about 62,000, we could see passenger loading over the whole day reaching 65% and 78% well before HS2 is due to open. What needs to be remembered is that not all seats on all trains are equial. In that having a seat on a train going to Liverpool is no good if you want to go to Manchester, likewise an empty seat at 21:00 is no good if you want to go at 12:00.
If you do the same for the 3 hour peak you end up with passenger numbers potentiall rising from about 8,000 to 12,000 (2017) and 14,000 (2020) each way, given that there is up to 14,000 seats (each way) in that period (FYI the arrivals into Euston in 2012 is only 12,225, but we'll leave that aside, however that may not be such an issue as the morning 3 hour peak groth rate is less between 2010 and 2012) that is a peak hour loading for ALL peak hour trains in 2020 of 100% (again that is assuming all seats on all trains are equial, which they are not). It is therefore likely that if growth does not fall away quite dramiticly over the next few years that the WCML will need other measures to cope with demand until HS2 is built.
Even if growth continues at the same rate of 6% until 2015 and then rises at 1% less per year until it reaches 1% growth (i.e. 6%, 5%, 4%, etc), then the passenger numbers in 2033 will still hit the HS2 target (the 1% growth rate is becuase that is comparable to the population growth rate of the UK). You get a similar result if the growth rate fell be 0.5% per year from 2012 till the growth rate hit 1% (i.e. 6%, 5.5%, 5%, 4.5%, etc), however it would reach the 2033 figure at in 2031 and you reach the 2026 figure in 2018.
Although that assumes that the growth rate still stays at 1% once HS2 Phase 1 is open (i.e. no new passengers use it beyond what would have done so anyway).
There is however a big risk (proberbly at least bigger than those listed above where the growth rate falls to 1%) that the passenger growth rate stays up above the 2.5% figure used in the model. No one has come up with what would need to be built (assuming HS2 is not built) to cope with the demand if passenger numbers hit more than 80% more than in 2009. That is the problem with the options put forward by the antis, there is no spare capacity if rail growth stays high.
It also doesn't need to stay high for long before it has a big impact on long term passenger numbers. As if you increase passenger number from 100 by 2% per year for 5 years you end up with 110 passengers (110.41 if you count part people), however if the growth rate is 4% you end up with 122 passengers (121.67 if you count part people), up it further to 6% and you end up with 134 passengers (133.82 if you count part people). Even if the growth rate then falls back to 2%, then after another 5 years the number of passengers is 122 (2% all the time), 134 (4% then 2%) or 148 (6% then 2%). That means that for just 5 years of double the growth rate you end up with about 10% more passengers overall than with flat growth, tripple growth (i.e. 6%) for the first 5 years and it is over 20% more passengers overall. Yes overtime the overall growth rate will start to flatten out, but you will still be left with about the same percentage of more passengers overall, although even that will start to increase slowly.
Given the coalition isn't going to canel it this side of the election, by which point we'll have the passenger numbers for at least up to 2014, if the passenger growth rate hasn't dropped off by very much (i.e. still more than 5%) then it is almost certain that HS2 will continue (almost regardles of who is in power) and possibly even accelerated. It is also possible that some more of the measures put forward by the anties as their way of meeting demand for 2033 will also be part of works for CP6 (i.e. for implimentation by 2025).