In reply to Rob Exile Ward:
Overcrowding on the south WCML i.e. the section between Northampton and London, and to a lesser extent commuter services around Brum. That's the main good reason for it, and the only one I support to any extent. There is little other justification, as most other capacity crunches, other than the south-of-London commuter lines which are almost impossible to fix because there's no more capacity and no more space to build lines, can be dealt with by way of longer or more frequent trains. Yes, even the appalling First Great Western - who runs 3 car commuter trains these days?
That it's being built as a high speed line is kind-of just that it might as well be one.
That said, we also need to invest in tram systems and electrification of commuter services, particularly around Manchester and Birmingham, and bringing them to European "S-Bahn" type standards.
Edit: And we need more home-working. Things like call centres and office jobs are perfect for that (and I hear Barclaycard have actually started doing it with their call centres).
Neil
Post edited at 13:18