Fake blood has been sprayed across the steps of the Treasury in central London by Extinction Rebellion protesters.

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The demonstrators parked an old fire engine outside the building and a pool of red liquid – said to be 396 gallons (1,800 litres) of water coloured with food dye – lay opposite the entrance.

Environment protest

Extinction Rebellion campaigners sprayed gallons of fake blood outside the Treasury in central London (Aaron Chown/PA)

Four protesters stood on top of the fire engine, which had a banner slung across it with the words “Stop funding climate death”.

Police said that four arrests have been made on suspicion of criminal damage. 

Meanwhile, the group's eagerness to cut the country's emissions by 2025 would do more environmental harm than good, a UK Government tsar has claimed.

Dieter Helm, chairman of the Natural Capital Committee advisory group, said reaching the environment campaigners' net-zero target would lead to an increase in pollution through imports.

Speaking in Edinburgh, the University of Oxford economics and energy policy professor said the group's target would do "a hell of a lot of damage" as carbon emissions would just be created elsewhere.

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He told the PA news agency: "The cost will be so colossally high because you would have to change all existing capital stock - public resistance would be extremely destructive to dealing with it.

"The only way to get emissions down really quickly here would be to stop Scottish industry then import the pollution - we will make the climate even worse."

The Herald:

The group have also protested in Scotland

Prof Helm instead argues a net-zero carbon consumption would be a more effective way to reduce pollution.

He used the example of British Steel, whose closure would see a reduction in emissions being created in the UK but would then lead to the product being imported from countries like China.

He said: "Your impact on global warming will be to increase it."

It comes as Extinction Rebellion prepares to announce 60 protests worldwide calling for action on the "climate emergency".

The campaigners are urging the UK Government to "act now to halt biodiversity loss" and reduce greenhouse gas emissions to net-zero by 2025.

They say the issue cannot be put off any longer by setting the date for decarbonisation at 2050.

The Herald:

Green MSP Patrick Harvie with a protester

The Scottish Government has set an earlier target, with legislation having been passed committing Scotland to net-zero emissions by 2045.

The Natural Capital Committee provides advice to the UK Government on the sustainable use of its natural resources.

This includes forests, rivers, land, minerals and oceans. Its remit also covers the benefits from natural assets, such as food, recreation, clean water, hazard protection and clean air.

Prof Helm has argued for a single-level carbon tax to be introduced and for those who contribute to a net reduction in pollution to receive payment.

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His three principles for a 25-year green plan are public money for public goods, polluters must pay, and there should be an environmental gain.

He said there has been a "wake-up call" that efforts to tackle climate change have not been working, but he believes his policies could create sustainable economic growth while also tackling global warming.

Prof Alston added: "Unless the environment is the core part we can't have sustainable economic growth, we can't have prosperity and we can't solve these problems."