Bird and conservation charity RSPB Cymru said the decision "sets a great precedent" for the future of Wales’ wildlife and the Wales that future generations will inherit.

Welsh Secretary Alun Cairns has told BBC Wales that it is a “dark day for Wales”.

He added: “It appears that the first minister thinks he knows better than the independent inquiry”.

Mark Drakeford will give a statement to the Welsh Assembly at around 2.45pm, not only explaining his decision to scrap the M4 relief road, but to outline the next steps.

Before then, he may be quizzed on the matter by assembly members during First Minister's Questions at 1.30pm.

We'll bring you the latest here throughout.

Karis Jones is an associate solicitor from Monmouth who uses the M4 every day to commute to court in Cardiff and Newport.

She said the rejection of the M4 relief road was "disappointing" and "frustrating".

"I would even have to consider potentially either moving to Cardiff, or potentially looking to move the other side Bristol way, actually moving outside of Wales”, she says.

Steffan Messenger
BBC Wales Environment Correspondent

Today's announcement by First Minister Mark Drakeford is a huge win for environmentalists and others who have long campaigned to protect the Gwent Levels.

It’s striking that Mark Drakeford says he attaches "very significant weight" to the environmental concerns, adding that he would have rejected the plans even if the costs of building the new motorway were lower.

It may not be the most famous of Wales’ beauty spots, but the wetlands south of Newport have been compared by campaigners to the Amazon rainforest in terms of biodiversity.

Rare birds, plants and insects have found a home here especially in the unique drainage ditches known as reens, dug during Roman times.

The first minister says the “substantial adverse impact” the plans would have had on nature could not be justified, contrary - we now know - to the conclusions of the public inquiry.

It may be a coincidence, but his decision also comes during Wales Nature Week and a day before the Welsh Government is set to mark World Environment Day at the Senedd.

Construction firms were hoping for a jobs boost from the M4 relief road.

Mark Bodger of the Construction Industry Training Board in Wales, said: "The M4 relief road would have led to a considerable increase in construction jobs in Wales, with valuable opportunities for skills and training.

The board is now planning to discuss other future construction projects with the Welsh Government.

Opponents of the relief road Friends of the Earth Cymru have called the decision "great news for Wales and the planet...

They add that "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."

Director Haf Elgar called for substantial investment in sustainable transport around Newport.

.

Business organisation CBI Wales calls the decision a "dark day for the Welsh economy".

Ian Price, director, said after decades of deliberation, no problem had been solved and congestion and road pollution around Newport could only increase.

Mr Price said while they struggled to see what alternative could be better than the M4 black route, "the ball is back in the Welsh Government’s court to deliver their Plan B".

He added: "An urgent and credible solution to the problem of congestion around the Brynglas tunnels must now be developed.”

Felicity Evans
BBC Wales political editor

The letter explaining the reasons for Mark Drakeford’s decision rejects the £1.4bn proposals on grounds of cost.

Mr Drakeford notes that the allocation of Welsh Government funds is beyond the scope of the public inquiry - which begs the question: why did the Welsh Government commission a public inquiry that cost tens of millions of pounds, when the Cabinet made the decision based on factors the inquiry could never consider?

The answer to that is the change of leadership at the top of the Welsh Labour.

Mark Drakeford was always cooler on the M4 relief road proposals than his predecessor, Carwyn Jones.

Nevertheless today’s decision marks an expensive U turn on his party’s 2016 manifesto commitment.

For emphasis, Mr Drakeford goes on to say that even if cost had not been an issue, he wouldn’t have gone ahead because of the environmental impact.

The Future Generations Commissioner Sophie Howe says: "All progress begins with a brave decision", saying it was "the right one for people and planet".

"Hope this marks a shift in policy for Wales and the Welsh Government now quickly bring forward investment in public transport," she adds.

Welsh Liberal Democrat Leader Jane Dodds said she was pleased the M4 relief road will not go ahead.

"We need to tackle congestion in South East Wales, but the M4 relief road is not the answer," she said.

"The financial and environmental costs are just too high.

The first minister has tweeted his decision to scrap the M4 relief road.

Plaid Cymru leader Adam Price said the party had warned for years that the black route would be a costly and environmentally damaging mistake but was met with ridicule from the Labour party.

Mr Price said indecision had "cost years better spent planning for alternative and sustainable improvements to the roads in Newport and the south east".

It has been revealed that the public inquiry inspector's report backed the scheme but concluded that "the allocation of Welsh Government funds was beyond the scope of the public inquiry".

As well as judging the project to be unaffordable, Mark Drakeford says he attached greater weight than the inspector to the risks to wildlife in the Gwent Levels.

Image source, Welsh Government

The former leader of the Welsh Conservatives in the assembly, Andrew RT Davies was a vocal supporter of the M4 relief road:

In his letter explaining his decision to scrap the M4 relief road, First Minister Mark Drakeford reveals that his cabinet decided several weeks ago that the scheme was not affordable.

Image source, Welsh Government

The First Minister's decision letter, external has been published on the Welsh Government website.

Dust, dirt and noise - in Newport some residents are hoping to get relief from a new motorway.

But others say it'll just move the problem elsewhere.

Plaid Cymru and the Liberal Democrats are against the plan, as is Future Generations Commissoner Sophie Howe.

The RSPB and the Gwent Wildlife Trust have also voiced their concerns.

Environmental campaigners have suggested that the Welsh Government's recent declaration of a climate emergency means they should scrap the plan.

Image source, Geograph/Jaggery

Speaking on BBC Radio Wales this morning, Welsh Secretary Alun Cairns said: “All the logic points to building this road as soon as possible."

He has previously said he understands that the public inquiry was in favour of the scheme.

CBI Wales, which represents business leaders, wants the new motorway to go ahead.

The newly formed Brexit Party group of 4 AMs is also keen.