A long-proposed £1.4 billion M4 relief road to ease congestion in South Wales has been scrapped, the Welsh Government has announced.

First Minister Mark Drakeford said the cost of delivering the project "was not acceptable" and expressed concerns about its effect on the environment.

The decision seemingly brings to an end 30 years of discussions in Wales about building a dual three-lane motorway south of Newport to relieve congestion on the existing M4 around the city.

Welsh Labour made building the road an election pledge in its 2016 manifesto under former leader Carwyn Jones, but Mr Drakeford made no mention of the project in his own leadership manifesto before succeeding him at the end of last year.

The Welsh Government ordered a £44 million public inquiry into the project, and a report by planning inspector Bill Wadrup, made public on Tuesday, backed the plans, saying it would provide good value for money.

But in his decision letter, also released on Tuesday, Mr Drakeford said his Cabinet had decided in April not to back the project due to demands on the Welsh Government's budgets and its financial position, saying the cost involved "was not acceptable".

He said the allocation of Welsh Government funds was "beyond the scope of the public inquiry" and not a matter on which the inspector should comment.

Mr Drakeford also said he attached "greater weight" to the effects that the road would have on the environment than the inspector had.

He said: "In particular, I attach very significant weight to the fact that the project would have a substantial adverse impact on the Gwent Levels SSSIs

and their green network and wildlife, and on other species, and a permanent adverse impact on the historic landscape of the Gwent Levels.

"As a result, in my judgment, the project's adverse impacts on the environment (taken together with its other disadvantages) outweigh its advantages."

Welsh Conservatives said the decision was a "kick in the teeth" for commuters and that Welsh Labour had "poured millions of pounds down the drain in completing the inquiry, only to ignore its findings".

Conservative AM Russell George said: "Congestion on this road is a foot on the windpipe of the South Wales economy, and is damaging our businesses and their future prospects."

Heather Myers, chief executive of South and Mid Wales Chamber of Commerce, said it and the business community it represented were "bitterly disappointed", while a joint statement from the Cardiff Capital Region City deal said south-east Wales would become "paralysed by an ageing transport infrastructure operating beyond capacity".

But Friends of the Earth Cymru said the decision was "great news for Wales and the planet", adding: "As well as costing Welsh taxpayers over £2 billion, this devastating road would have ploughed through the unique, wildlife-rich Gwent Levels, pumped more climate-wrecking emissions into our atmosphere, and ultimately caused even more congestion and air pollution."