WESTMINSTER has no right to pursue plans to build an M4 bypass around Newport, the Welsh Government said today in response to a new piece of legislation proposed by Downing Street.

The Internal Market Bill, published today (Wednesday), will "preserve the status quo of seamless internal trade" between Wales, England, Scotland and Northern Ireland after the Brexit transition period, the UK government said.

But away from England, the bill has come under fire, with accusations Westminster is threatening the rights of the devolved administrations in Wales and elsewhere.

The bill threatens to reignite the long-running debate over traffic problems on the M4 around Newport, too, thanks to a section that says a UK government minister may use parliamentary funds to assist with "promoting economic development" or "providing infrastructure" in any area of the UK.

The language in the bill suggests Westminster could technically use this rule as a means of reviving the plans for a relief road around Newport – even though transport is an area over which the devolved Welsh Government has control.

Boris Johnson's Conservative government has flirted in the past with the idea of building the M4 bypass, and earlier this week the Welsh Conservatives reiterated the Senedd party group's support for the project abandoned by the Labour-led Welsh Government last June.

Responding to the UK government's Internal Market Bill, a Welsh Government spokesman said: “We believe in the principle of an internal market – but this bill is not remotely necessary to deliver it. We will do everything we can to challenge the power grab and the race to the bottom which this bill represents.

“The M4 is a matter for the Welsh Government, not Westminster, and our decision has already been made. We remain committed to tackling congestion with solutions that recognise the unprecedented challenge of climate change as well as the financial pressures caused by 10 years of austerity and capital budget cuts.”

The UK government said the new bill will give Wales and the other devolved nations “power over more issues than they have ever had before”, but others have interpreted the bill to pose a threat to devolution.

Jeremy Miles, Wales' Brexit minister, said: “Let me be clear – the UK government plans to sacrifice the future of the union by stealing powers from devolved administrations.

“This bill is an attack on democracy and an affront to the people of Wales, Scotland and Northern Ireland, who have voted in favour of devolution on numerous occasions.”

Plaid's Delyth Jewell, MS for South Wales East, has previously condemned the prime minister's efforts to talk up a renewed relief road project for the Newport area, saying he would risk "picking the mother of all constitutional battles".

Reacting to the Internal Market Bill, she said: “Devolution has received 14 mandates from the people of Wales in two referendums, five Senedd elections and seven general elections since 1997, all of which have returned clear pro-devolution majorities.

"Attempting to overturn this by decree is outrageous and undemocratic."