T he arguments against HS2 are simple, and superficially attractive: why are we spending £55bn on a high-speed line between London and the north, when commuters outside the southeast are cramming onto unreliable, expensive, and infrequent old trains?

The latest polling shows the new railway is unpopular, and Tory leadership wannabes are circling to scrap it, hoping to win the affections of their party members, who hate it even more than the general public.

The government has failed to make the case for HS2. So allow me to make it here, because it’s actually a very good idea.

Those concerns about overcrowded, creaking commuter trains are real: but they cannot be solved without HS2, or something extremely similar. The problem is that explaining why is quite complicated, so politicians haven’t really tried.

Some people seem to think HS2 is about “knocking 35 minutes off London to Birmingham”. It isn’t. Yes, it will dramatically reduce journey times: the whole project will cut London-Manchester from two hours to one; it takes around an hour off the journey to Scotland; Birmingham to Newcastle is cut from three hours 15 minutes down to two hours. Birmingham to Nottingham, which currently takes over an hour, falls to an almost ridiculous 19 minutes. One misconception is that these will be special “high-speed” premium services with higher ticket prices for rich passengers. That isn’t true – these will be the ordinary journey times between those cities, integrated into the existing network.

But speed is not the main point of the new line. The objective is capacity, and not just capacity for fast intercity services, either, but for those local regional and commuter services between small towns that have been so neglected. The complicated bit is explaining why that is.

Britain’s railways were largely built in the Victorian era, for a different kind of travel. Today, the same lines carry a mix of express intercity trains – the kind which HS2 will take – and stopping local and commuter services, the kind people use to get to work, or pop to a neighbouring town.

This mix is a very inefficient way to run a railway, for a reason that is quite obvious if you think about it: trains cannot overtake each other on the same set of tracks. They would bang into the back of one another if they tried. Not good. To get around this, local stopping trains need a large gap behind them in the timetable, so the express trains behind them do not catch up. That reduces the number of trains you can have per hour on a line, dramatically reducing its capacity for every type of service – local and express.

Extinction Rebellion: Climate change protests cause chaos in London Show all 46 1 /46 Extinction Rebellion: Climate change protests cause chaos in London Extinction Rebellion: Climate change protests cause chaos in London Canary Wharf A protester gives a thumbs up as he stalls a DLR train at Canary Wharf station in London Reuters Extinction Rebellion: Climate change protests cause chaos in London City of London Protesters hold up traffic on Upper Thames Street in the City of London Getty Extinction Rebellion: Climate change protests cause chaos in London Canary Wharf Protesters hold a banner as they hold up a DLR train at Canary Wharf station in London Reuters Extinction Rebellion: Climate change protests cause chaos in London Waterloo Bridge Officers remove plants that were placed in the occupation of Waterloo Bridge PA Extinction Rebellion: Climate change protests cause chaos in London Oxford Circus Police officers arrive at Oxford Circus as they prepare to remove protesters during the fifth day of a coordinated protest by the Extinction Rebellion group, April 19 Getty Extinction Rebellion: Climate change protests cause chaos in London Waterloo Bridge An activist waters the plants at the occupation on Waterloo Bridge PA Extinction Rebellion: Climate change protests cause chaos in London Heathrow airport Undeterred by over 400 arrests, climate change activists continued their demonstration into a fifth day in London with a small protest at the country's main Heathrow Airport, along with the ongoing protest camps at other iconic locations around the British capital Reuters Extinction Rebellion: Climate change protests cause chaos in London Oxford Circus Protesters with the words 'glued on' written on their hands hold hands as police officers arrive at Oxford Circus Getty Extinction Rebellion: Climate change protests cause chaos in London Waterloo Bridge Officers circle the lorry that serves as the central stage to the Waterloo Bridge occupation, repeating their tactic from a earlier at the Oxford Circus occupation Reuters Extinction Rebellion: Climate change protests cause chaos in London Oxford Circus Oxford Circus reopens after being closed for days due to occupation AFP/Getty Extinction Rebellion: Climate change protests cause chaos in London Waterloo Bridge Officers prepare to move in on the occupation of Waterloo Bridge PA Extinction Rebellion: Climate change protests cause chaos in London Waterloo Bridge Activists relax on a sofa at the occupation on Waterloo Bridge AFP/Getty Extinction Rebellion: Climate change protests cause chaos in London Oxford Circus British actress Emma Thompson talks to members of the media from atop the pink boat after police officers surrounded the boat being used as a stage as climate change activists occupy the road junction at Oxford Circus in central London during the fifth day of environmental protesst by the Extinction Rebellion group AFP Extinction Rebellion: Climate change protests cause chaos in London Waterloo Bridge An Extinction Rebellion demonstrator is carried away by police on Waterloo Bridge PA Extinction Rebellion: Climate change protests cause chaos in London Waterloo Bridge Activists on Waterloo Bridge have made a garden for their occupation site, April 20 Reuters Extinction Rebellion: Climate change protests cause chaos in London Oxford Circus Demonstrators began blocking off a bridge and major central road junctions on April 15 at the start of a civil disobedience campaign calling for governments to declare an ecological emergency over climate change, to reduce greenhouse gas emissions to zero by 2025, halt biodiversity loss and be led by new "citizens' assemblies on climate and ecological justice" Reuters Extinction Rebellion: Climate change protests cause chaos in London Oxford Circus Emma Thompson joins the Extinction Rebellion protest at Oxford Circus. Thompson spoke from the pink boat at the centre of the occupation AFP/Getty Extinction Rebellion: Climate change protests cause chaos in London Heathrow airport Extinction Rebellion protesters sit outside Heathrow Airport on April 19 Reuters Extinction Rebellion: Climate change protests cause chaos in London Heathrow airport Climate protestors hold a demo outside Heathrow Airport Getty Extinction Rebellion: Climate change protests cause chaos in London Waterloo Bridge Police officers detain a climate change activist at Waterloo Bridge Reuters Extinction Rebellion: Climate change protests cause chaos in London Marble Arch Protesters prepare for another day at Marble Arch as the Extinction Rebellion protests enter their fifth day Getty Extinction Rebellion: Climate change protests cause chaos in London Oxford Circus British actress Emma Thompson gives an address from the stage atop the pink boat AFP/Getty Extinction Rebellion: Climate change protests cause chaos in London Oxford Circus Actress Emma Thompson takes a photo with a Extinction Rebellion demonstrator PA Extinction Rebellion: Climate change protests cause chaos in London Oxford Circus Climate change activists blockade Oxford Circus on the third day of an environmental protest by the Extinction Rebellion group AFP/Getty Extinction Rebellion: Climate change protests cause chaos in London Waterloo Bridge Climate change activists stand atop a bus shelter as they take part in a blockade of Waterloo Bridge AFP/Getty Extinction Rebellion: Climate change protests cause chaos in London Canary Wharf Police is seen as climate change activists demonstrate during the Extinction Rebellion protest, at Canary Wharf DLR station in London Reuters Extinction Rebellion: Climate change protests cause chaos in London Waterloo Bridge Police speak to climate change activists blockading Waterloo bridge AFP/Getty Extinction Rebellion: Climate change protests cause chaos in London Waterloo Bridge epa07511673 A demonstrator gestures the hand heart as protesters from the Extinction Rebellion campaign group block Waterloo Bridge in central London, Britain, 17 April 2019. The Extinction Rebellion are holding a number of protests across London to draw attention to climate change. EPA/NEIL HALL NEIL HALL EPA Extinction Rebellion: Climate change protests cause chaos in London Waterloo Bridge Climate change activists, one (right) with her hand glued to the underside of a truck parked across Waterloo Bridge AFP/Getty Extinction Rebellion: Climate change protests cause chaos in London Oxford Circus Environmental campaigners protest in the centre of Oxford Circus Getty Extinction Rebellion: Climate change protests cause chaos in London Jeremy Corbyn's Home Climate change activists from Extinction Rebellion protest sit after glueing themselves to the front fence of Britain's opposition Labour Party leader Jeremy Corbyn's house Reuters Extinction Rebellion: Climate change protests cause chaos in London Marble Arch Dozens of tents have been pitched at Marble Arch in a large scale occupation Reuters Extinction Rebellion: Climate change protests cause chaos in London Canary Wharf station Police remove climate activists who glued themselves on top of a train at Canary Wharf station EPA Extinction Rebellion: Climate change protests cause chaos in London Oxford Circus Police forces carry a protester AP Extinction Rebellion: Climate change protests cause chaos in London Canary Wharf station A climate change protestor who glued his hand to a window halts a DLR train AFP/Getty Extinction Rebellion: Climate change protests cause chaos in London Waterloo Bridge Extinction Rebellion demonstrators on Waterloo Bridge, London, after police issued a Section 14 Public Order Act 1986 warning. PRESS ASSOCIATION Photo. Picture date: Wednesday April 17, 2019. See PA story ENVIRONMENT Climate. Photo credit should read: Jonathan Brady/PA Wire Jonathan Brady PA Extinction Rebellion: Climate change protests cause chaos in London Waterloo Bridge epa07512336 Extinction Rebellion climate change demonstrators protest on Waterloo Bridge during climate change protests in London, Britain, 17 April 2019. The Extinction Rebellion are holding a number of protests across London to draw attention to climate change. EPA/ANDY RAIN ANDY RAIN EPA Extinction Rebellion: Climate change protests cause chaos in London Waterloo Bridge epa07512368 Extinction Rebellion climate change demonstrators protest on Waterloo Bridge during climate change protests in London, Britain, 17 April 2019. Waterloo Bridge remains closed as protests continue. EPA/ANDY RAIN ANDY RAIN EPA Extinction Rebellion: Climate change protests cause chaos in London Oxford Circus Extinction Rebellion demonstrators in Oxford Circus, London, as more than 200 people have been arrested as police deal with ongoing climate change protests. PRESS ASSOCIATION Photo. Picture date: Wednesday April 17, 2019. See PA story ENVIRONMENT Climate. Photo credit should read: Kirsty O'Connor/PA Wire Kirsty O'Connor PA Extinction Rebellion: Climate change protests cause chaos in London Oxford Circus LONDON, ENGLAND - APRIL 17: An Environmental campaigner is carried by police officers at Oxford Circus during the third day of a coordinated protest by the Extinction Rebellion group on April 17, 2019 in London, England. More than 100 arrests have been made, with demonstrations blocking a number of locations across the capital. (Photo by Leon Neal/Getty Images) Leon Neal Getty Extinction Rebellion: Climate change protests cause chaos in London Waterloo Bridge Pedestrians and a cyclist pass graffiti drawn by protestors who blocked Waterloo Bridge AP Extinction Rebellion: Climate change protests cause chaos in London Waterloo Bridge Climate change protestors practice yoga on Waterloo Bridge AFP/Getty Extinction Rebellion: Climate change protests cause chaos in London Waterloo Bridge A climate change activist gestures while being detained by police officers Reuters Extinction Rebellion: Climate change protests cause chaos in London Waterloo Bridge Protestors sit on the road AP Extinction Rebellion: Climate change protests cause chaos in London Waterloo Bridge Extinction Rebellion demonstrators on Waterloo Bridge, London, as more than 200 people have been arrested as police deal with ongoing climate change protests. PRESS ASSOCIATION Photo. Picture date: Wednesday April 17, 2019. See PA story ENVIRONMENT Climate. Photo credit should read: Yui Mok/PA Wire Yui Mok PA Extinction Rebellion: Climate change protests cause chaos in London Oxford Circus Police forces carry a protestor to arrest him at Oxford Circus in London, Wednesday, April 17, 2019. The group Extinction Rebellion is calling for a week of civil disobedience against what it says is the failure to tackle the causes of climate change. (AP Photo/Frank Augstein) Frank Augstein AP

The engineering thinking behind HS2 is to take those express services off the older mainlines, leaving them for stopping local and commuter services. When trains are all travelling at roughly the same speed on a line, you can fit a lot more in, because the gaps needed between them are smaller.

HS2 will take express trains off the West Coast Main Line that links London with Birmingham and the cities of the northwest; the Midland Main Line that links London with the East Midlands and Sheffield; and to an extent the East Coast Main Line that goes up to Leeds and Newcastle. That frees up capacity across a huge swathe of the country for local services, and it’s the whole rationale behind the project. That the government hasn’t been explaining this ad nauseum is inexcusable.

Protests against HS2 have been fierce every since the project was open to a public consultation in 2010 (Getty) (Getty Images)

So if the plan is to improve commuter services, why not build a new commuter line instead of a new one for expresses? It wouldn’t make sense: these existing lines are already good for slow trains, and they go into the centres of towns and cities, which have since expanded around them. A new high-speed line for expresses can make use of engineering advances since the 19th century to speed up journeys, and doesn’t have to go into as many built up areas as a local line would, where the need for tunnelling and demolitions would make it more expensive and disruptive. And making a line high-speed doesn’t actually cost that much more, either, if you’re building one anyway. But the key point is that local services benefit, despite the new line being for express trains.

HS2 will also bring other direct benefits to cities and towns that aren’t London. Northern Powerhouse Rail (stupid name) is the government’s plan to connect up the cities of the north of England with high-speed rail. It’s currently in development, but the plan, as put together by northern councils, relies on vast sections of HS2 track. Liverpool to Manchester; Sheffield to Leeds and towards York and Newcastle – these bits of NPR will use parts of HS2.

The government arguably made a huge mistake by starting planning on the NPR scheme so late, leaving people wondering why they were prioritising journeys to London – but with Labour and the Conservatives both committed to the project, it is likely to happen. HS2 and better connections between non-London cities aren’t an either/or: the two projects are intrinsically linked. If HS2 is scrapped, who knows when a government will next be brave enough to try a major rail project again.

Rail minister Andrew Jones says HS2 will be key part of strategy to fix capacity problems for trains

In the meantime, the West Coast Main Line is filling up, and can’t wait. The reason ticket prices are a rip-off from London to Manchester (£175 for a walk-up, one-way, anytime ticket is absurd no matter what cheap advance fares are available – sometimes you just have to travel) is because the trains are running completely full and Virgin can charge what they like and still have a passenger in every seat – and sometimes the floor. The number of passengers using the route doubled between 1997 and 2005, and it is well on its way to doubling again. The huge capacity increase that HS2 brings is a response to that.

It’s understandable that people are sceptical of a project that has been badly explained, when it isn’t obvious why it deals with the biggest problems they see with the railways. That said, some criticisms are red herrings. Take the environmental impact: over the 140 miles of HS2 line, 29 hectares of ancient woodland will be felled. Sounds bad? But for comparison, a single 2.5-mile road scheme, widening the A21 in Kent and Sussex (not even a new road!), will take down nine hectares, around a third of HS2’s phase 1 total. Extinction Rebellion are barking up the wrong tree on this one; far more road schemes will be needed if we can’t shift traffic to more efficient rail, and that means building more capacity. High-speed rail has also proven the greenest way to get people off short-haul flights, dominating routes like London-Paris or Madrid-Barcelona, where polluting planes would otherwise be king. Long term, it’s good for the environment. And new trees are being planted elsewhere to replace the ones cut down.

Any large project will be disruptive, but compared to the other options, HS2 is actually pretty good. Consider one much-touted alternative: upgrading the West Coast Main Line with an extra pair of tracks for more capacity. There are several thousands houses built facing onto the line, and you’re going to need to knock them down to put a railway there. And it won’t be high-speed, it’ll be more expensive to do it, and it’ll be massively disruptive – not just for people losing their homes, but passengers who would face about a decade of closures and replacement buses. The more general problem with suggestions that existing lines should simply be “upgraded” (a rather vague proposal) is that there are simply diminishing returns to what you can do with 150-year old infrastructure. The West Coast Main Line already benefited from a major upgrade programme ending in 2005; it took a decade of disruption and cost over £10bn in today’s money, provided only a fraction of the benefits of HS2, and is already full. Plans to upgrade it further were abandoned because they weren’t seen as practical, and planning for a new line that became HS2 is a direct result of that process.