OK, I'll try. But I'm very reluctant, because there's such an emotional hatred of HS2 here, and I'm sure I'll get flamed from every angle. But there has to be a reason why £50bn has been thrown at this, it can't purely be a vanity project. So please, don't all tear into me at once.
The thing is, the Northern railway lines are desperately low on capacity. A high-speed train has a minimum safe gap between trains of at least 5 miles. What you find is that within that gap, you can fit 4 suburban trains. So if you put the fancy high-speed trains in their own track, instead of running 1 train per hour from Macclesfield to Manchester, you can run 3 or 4.
Of course, there are other ways of boosting capacity. Run longer trains, for example. But then you need to increase platform lengths. Improve the signalling systems, so trains can run closer together. Actually that's not a bad idea, and they're also doing that. Build more railway lines in the North? That's expensive and controversial. You think building one line brings out an army of protestors, try building 10. Upgrade existing railway lines? Not so effective if the train has to sit in a siding waiting for the Inter-City to come thundering through.
Broadly speaking, I'm a supporter. But fuck me, the cost is eye watering. I'll get my hard hat.