Friends of the Earth Cymru have confirmed today that a letter will be sent to the Welsh Government, asking them to withdraw and restart an environmental consultation about the proposed M4 relief road route.
The group say they are concerned about the environmental impact of the proposals, and claim alternative routes to the one through the Gwent Levels - which was announced as the preferred road earlier this month - were not given enough consideration.
The Welsh Government has two weeks to respond to the letter, and depending on the outcome of that, Friends of the Earth may decide to then begin judicial review proceedings.
Ministers have previously said they expected to face a legal challenge.
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The rain will clear up this evening, leaving a fairly quiet night to come with some pretty mild temperatures overnight.