Even through the mist of the French Pyrenees, a mile above sea level and 600 miles south of Westminster, Britain looks a mess.

French, Spanish and German hikers in the gite d’étape (mountain hostel) regard the British with mirth, mingled with sympathy and concern.

They cannot believe that a once liberal, tolerant country is – in one of the many paradoxes triggered by Brexit – simultaneously tearing itself apart while at the same time trying to erect barriers.

As backpacks are strapped on and and boots are laced tight, our continental counterparts demonstrate remarkable knowledge of the purge of ex-ministers by the UK government and the ineptitude of Her Majesty’s Loyal Opposition.

There are many dangers of Britain’s present political disarray. One serious risk is that the extreme short-termism of power-hungry politicians will cause lasting damage to the UK. And a prime example is the threat to High Speed 2.

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As you may know, HS2 is the scheme to build a new Y-shaped railway connecting London with Birmingham (phase one), with a western arm extending to Manchester and an eastern branch to Leeds (phase 2). Some trains will continue on to Liverpool, Glasgow and Edinburgh on the existing west coast main line, while York, Durham and Newcastle will be served via the northern part of the east coast line.

You may be strongly against the project – especially in a week when the chairman of HS2, Allan Cook, published what he called a “Stocktake” of the project. He warns of “an upward revision of the funding envelope”, which in English means that phase one will cost 40 per cent more than the original estimate of £27bn, and phase two 25 per cent on top of the original £28.6bn.

Let’s call it £80bn – a staggering amount of money for a rail project in a country where many people rarely or never travel long distances by train.

Cook also called the plan to open phase 1 as planned in 2026 “not viable”.  Trains are now timed to depart on the full London-Birmingham line five years behind schedule, with the Leeds and Manchester arms as late as 2040.

Twelve years from now, there could be two ceremonies involving high-speed rail in adjacent countries. The French will be marking half a century since the first Train à Grande Vitesse ran on the line from Paris to Lyon, in 1981. The British, meanwhile, may be celebrating the completion of the first domestic-only high-speed link.

Hopelessly optimistic budgets and schedules for big rail projects are nothing new; the recent electrification of the Great Western lines and London’s much-delayed Crossrail project were both seriously botched.

Yet HS2, or something like it, will be desperately needed in generations to come. It is not about accelerating the journey from Birmingham to London by 20 minutes, though that will have some environmental and social benefits in shifting travellers from rail to road.

The purpose of the new line is to increase the capacity of a 19th-century railway network to make it fit for the 21st century – or however much of it remains when the line finally opens.

Each inter-city train transferred from existing lines to High Speed 2 will release, it is claimed, “capacity for 11 new fast commuter or freight trains” by taking out the fastest services.

Cancelling the whole thing, into which at least £7bn has already been sunk, would undoubtedly be a vote-winner in constituencies where the bulldozers are poised. It would also play well in regions such as southwest England, South Wales and East Anglia which will see no direct benefit from HS2.

But most of the tens of millions of people in the 2040s, 50s and beyond who will need the increased capacity are not yet on the electoral register.

At a time when some politicians appear desperate for power, and hence votes, at any cost, visionary infrastructure projects are as dispensable as distinguished parliamentarians.

HS2 has thus far been poorly specified, planned and managed. Like our politics, it is a mess. But it is still essential.