The road to hell is paved with good intentions, and in his budget the chancellor, Rishi Sunak, headed off down the motorway towards climate catastrophe, all the while proclaiming his intention to protect the environment.

“Over £27bn of tarmac,” he announced, for 4,000 miles of major new roads. In stark contrast, low-carbon transport was put in the slow lane, getting £1bn.

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Worse, Sunak flunked a golden opportunity to end the decade-long freeze on fuel duty that has pushed up traffic and pollution and suppressed bus and train travel. The oil price is now plummeting; even if the duty had been raised, drivers might not have seen any change in the price at the pump.

Transport emissions are now the biggest contributor to the UK’s carbon emissions and they are rising; 90% come from the roads.

Emissions from transport are a key reason the government is on track to miss its own legally binding carbon targets.

The other key reason is the UK’s terribly energy inefficient buildings, which lose heat up to three times as quickly as homes in neighbouring countries. Making homes cleaner, cosier, and cheaper to heat is a no-brainer. Yet there was not a single word on this in Sunak’s speech or the 125-page budget document.

This failure really matters, with the UK hosting a crucial UN climate in just eight months’ time. The summit – Cop26 in Glasgow – is a pledging party at which the world’s nations must offer much bigger emissions cuts to head off the climate crisis. The host needs to start the party with a splashy pledge, but Sunak just tossed in a crumpled fiver found in a back pocket.

There will be more opportunities to show a lead before November, with the long-delayed national infrastructure plan, the comprehensive spending review and the Treasury’s net zero review all to come.

But this is a year of consequences and the perennial problem of postponing serious climate action in the face of the latest short-term problem cannot continue, whether because of coronavirus or Brexit.

There were some green announcements in the budget, but they were nearer the bare minimum than world-leading. Flood defence spending was increased, but only after recent deluges and dire warnings of unpreparedness from the government’s own advisers.

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Carbon capture and storage (CCS) plants, where emissions from fossil fuels are trapped and buried, are likely to be very important in tackling the climate emergency and £800m is serious funding. But the dates for establishing two CCS sites – 2025 and 2030 – are very late. Global emissions must already have halved by 2030 to avoid the worst climate impacts. The cancellation of the £1bn CCS fund by the Conservatives in 2015 looks very shortsighted now.

“Over the next five years, we will plant around 30,000 hectares of trees,” said Sunak, referring to part of the £640m over five years designated for a “nature for climate” fund to store carbon.

But the advice of the official advisers, the Committee on Climate Change, is for 30,000 hectares each year, while the Green Alliance says £800m a year is needed to enhance natural habitats.

The plastic packaging tax, and cuts to red diesel subsidies, are sensible, but hardly transformative, and the latter is now riddled with loopholes.

In the £1bn for clean transport was £500m to help build a network of rapid chargers for electric vehicles so that no one will be more than 30 miles from a charger. There was also £400m to partially reverse cuts in subsidies for plug-in electric cars. These are dabs on the brake of carbon emissions.

But the fact that the UK will not ban the sale of new petrol and diesel vehicles until 2035 – later than other nations – plus the real-terms price cut for fuel and the extraordinary road building bonanza is stamping on the accelerator.

Sunak said that, as well as dealing with coronavirus, the budget “was a plan for prosperity tomorrow”.

The only prosperous future is zero carbon, but drawing the roadmap to get there requires tough choices – above all ruling out policies that lock in emissions.

Once again, the government has been waylaid by diversions of political expediency. The journey to net zero just got longer and more painful.