I'm in two minds. £33 billion is a hell of a lot of money (well, three Olympic Games, anyway...). It's arguable whether we really need a high-speed network in Britain - it makes sense in France because its a big country (3 times the size of GB) and the major cities are a long way apart, separated by lots of relatively empty space, but in the UK cities are closer together and the space between isn't really empty, which means that to be useful to most people you need more frequent stations, which means that trains would have to keep accelerating and decelerating so you don't get up to very high speed for very long.
On the other hand, the existing routes are predicted to be full in the next 20 years are so, and contrary to some other peoples' answers, the solution is NOT longer trains - in many places you just can't run longer trains without fouling junctions at stations, fitting on platforms, etc Only about ten years ago £10 billion was spent on the West Coast line to introduce new signalling which would allow 140 mph trains to run, and they couldn't get it to work, which is why trains are still restricted to 125 mph even though Pendolinos are designed for 140. I've just read this weeks' Crewe Chronicle which explains the proposals as they affect Crewe, and apart from putting the main Manchester HS2 line in a tunnel under the town, they're going to put in a junction between HS2 and the existing WCML just south of Crewe, so trains from Liverpool / Preston / Glasgow etc will be able to get to London about 30 minutes faster than they can on the existing route. Crewe to London in 58 minutes is quite impressive - 15 years ago it usually took 135 minutes, and it takes around 90 minutes now. Oh, and Alan B, HS2 won't knock 15 minutes off the London to Manchester journey time, it'll knock an hour off the existing 2 hour 7 minutes schedule.
On the third hand, quite a large part of Camden will need to be demolished to make way for the new route and the new Euston station.