There’s an understandable tendency to look at high speed rail as a way of getting to London more quickly.

But the importance of the proposed £33 billion line goes far beyond that. It is designed, eventually, to be a national network which will link together London with the West Midlands, the East Midlands, the North East and the North West.

That means stations in Manchester and Leeds, as well as at a location yet to be decided in the East Midlands.

But it also means stations in places like Liverpool, Wigan and York will receive services, even though they are not on the high speed line itself.

Trains capable of running on both high speed and conventional track will go to these destinations - travelling at high speeds for much of the journey before turning off and heading to the station on a conventional line.

It’s a clever idea which means even towns and cities not on the high speed line can benefit directly from the new network.

But plans for these hybrid services have been quietly downgraded, as we report.

Details were published in official Department for Transport documents setting out the economic case for HS2 last February. The fact that the new line will connect towns and cities across the country is indeed an essential part of the economic case.

But changes to the plans have been quietly introduced and published in a new, updated appraisal of the benefits.

It’s true that nothing so far has been set in stone. Indeed, no decisions whatsoever have been made about the route of the line north of the West Midlands - known as phase two - beyond the simple fact that the Government says it is committed to building it.

But clearly the Department for Transport must have some idea what’s planned, otherwise it wouldn’t be able to argue that building the second phase made sense at all. And the value for money reports make it clear that routes are being drawn up, and changed, with very little public debate.

For Labour, the answer is clear. The hybrid Bill set to come to the House of Commons before the next election should authorise the construction of both phases of the line, not just phase one as the Government plans.

This wouldn’t mean the whole thing would be built in one go. Clearly, constructing a new national rail network will take time and it probably does make sense to open it in phases.

But it does mean that the whole network would be discussed in one go, rather than MPs being asked to authorise the first half before they have seen full details of the second half.

And looked at this way, MPs such as Richard Burden make a strong case. The justification for going ahead with phase one is largely that it is part of a larger project. In other words, without phase two, the case for phase one is much weaker.

So how can Parliament be expected to authorise phase one when it hasn’t even seen confirmed, firm details for phase two?

Set aside questions about the wider network must be the undoubted advantages to Birmingham of creating a new rail network which we know will provide much-needed rail services to a number of major destinations.

The existing inter-city service, the West Coast Main Line, can hardly cope with demand as it is. A new rail line is needed.

But Ministers must provide more clarity about what exactly the entire network will look like, including services north of the West Midlands, before they expect Parliament to approve it.