A green think tank has warned of the risk of unintended consequences from the wave of concern about plastics.

The Green Alliance, a parliamentary group, said plastics played a valuable role and couldn't be simply abolished.

It wants to transform the notion of a "War on Plastics" into a "War on Plastic Litter".

The group - like many environmentalists - gave a grudging welcome to Chancellor Philip Hammond's call for evidence on taxes on single use plastics.

But it warned that rejecting all plastic food packaging could prove counter-productive.

Agriculture is a major source of greenhouse gas emissions, so reducing food waste is vital.

Well-packed food - perhaps in plastic - helps protect food from damage, so it can actually save on greenhouse gases.

Finite land

The other potential area of concern is the substitution of plastics with plant-based materials.

Forests are already being felled to grow crops to feed the world's booming demand for meat production and wild land is also disappearing to produce bio-fuels for cars and electricity generation. But there is a finite amount of land.

The Green Alliance fears that a demand for plastic substitutes could also increase the pressure for deforestation.

This would, in turn, lead to more greenhouse gases that would warm and acidify the oceans people are anxious to protect.

The Green Alliance's Libby Peake told BBC News: "Plastics are clearly a huge problem but we have concerns that legitimate public outrage will lead businesses and governments to rush into the wrong decisions.

"We must ensure that whatever solutions we design don't increase emissions, damage world ecosystems or result in more waste."

The public backlash against plastics led Lego to announce that in future it will make its toys from plastics derived not from oil, but from sugar cane.

It won the headline: "Lego goes green one brick at a time". But the firm confirmed to me that the "eco" bricks would be made from polyethylene - that's exactly the same chemical compound as plastic derived from oil (which, of course, came from plants millions of years ago).

The environment-friendly bricks will last just as long and be just as hard when you tread on them in bare feet.

Marine pollution

The firm told me: "The bio-based plastic used is produced from renewable sources and it meets the Lego Group's requirements for play value, quality, safety and durability."

Ms Peake said: "Turning plants into plastic in this way means that, at the end of life, it won't be biodegradable and will have all the potential drawbacks of traditional plastic.

"In other words, it won't do anything to solve the crisis of marine pollution.

"Lego has done everything right to try to sustainably source material for its bio-bricks. But there's clearly nowhere near enough sugar cane that can be sustainably sourced if other companies want to follow suit."

Read more on bbc.com.