Not a single penny of Labour’s proposed £500 billion infrastructure investment boost should be spent on items that increase carbon emissions, the shadow Treasury minister leading the party’s review to “green” government spending has said.

Clive Lewis, who is a former shadow secretary of state for business and energy, has been tasked by Labour with looking at how spending decisions are assessed against the need to tackle climate change and protect the environment.

During a question and answer session at a Labour party conference fringe event last week, Lewis said shadow chancellor of the exchequer John McDonnell had invited him to join the Treasury team specifically to carry out the exercise.

He said: “John likes to have an environmental sustainability guy at the Treasury to make sure we don’t spend a penny on things that add carbon and are going to be unsustainable.”

The Norwich MP said £500 billion, which Labour has pledged to earmark for infrastructure if it is elected to government, would need to be used in a “very sustainable ecological way.”

He questioned the wisdom of building new infrastructure, like airports, which increases carbon emissions in the light of predictions that the world must halve its production of greenhouse gases over the next decade in order to prevent runaway climate change.

Lewis said the exercise involved a fundamental rethink of the mindset of the Treasury, which many environmentalists blame for the wide-ranging cutbacks to sustainable energy subsidies following the 2015 election.

The Treasury would have to take greater account of sustainability and decarbonisation beyond what he described as its existing focus on revenue maximisation, he said: “If we are talking about plans to be able to tackle sustainability, the dynamics of Treasury are going to have to shift in the way they think of the long term.”

As part of this rethink, Lewis mooted that Labour may create a new shadow Treasury cabinet post as a counterweight to the portfolio of the chief secretary of the Treasury, who is responsible for vetting government spending decisions.

“There is an argument to have a third person in the shadow Treasury team who sits in cabinet and makes sure that every penny spent you get decarbonisation.”

Responding to a question on the government’s recent decision not to replace the feed-in tariffs scheme, he also raised concerns that investors had lost confidence in the UK’s low carbon policy.

“Investors have completely lost confidence in renewables especially with the decisions on onshore wind: from an investment point of view this is not a good market.”

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