Simple. Big infrastructure projects employ people and keep the country ticking over. Also, this is not really about saving x minutes from A to B, it is about expanding capacity in general. Our railways are overloaded on the main routes.

I don't like HS2 as it has no stations between London and Birmingham (I understand why, but they could engineer some extra long sidings for 'slow' trains. However, we need to build more infrastructure, this should have been done 20 years ago as the French did. What is the alternative? We end up with problems like Heathrow/London airports capacity/becoming uncompetitive in the global market.

I also think the government should invest in more tram and urban transit projects in general. Trams linked from park&ride stations to city centre etc. Much disruption to local traffic while work is underway, but it is the right thing to do to create a better environment in our cities.