A DECISION must be made on the long-awaited M4 relief road as soon as possible, MPs have said.

AMs are expected to get a vote on the scheme early next month, with Carwyn Jones due to make the final decision before he leaves office on Tuesday, December 11.

Chancellor Philip Hammond announced in his autumn budget the Welsh Government could be offered £300 million in borrowing if it is spent on the road - leading to accusations the UK Government was attempting to force Welsh ministers to give the project the green light.

MPs discussed the issue in Parliament last week, where Monmouth MP David Davies said he believed "the only solution" to traffic problems on the stretch of the M4 running past Newport was the so-called black route, which would involve an entirely new stretch of motorway running south of the city, bypassing the often-congested Brynglas Tunnels.

"I am concerned not just about the increase in traffic that we will see as a result of the Conservative Government’s welcome decision to end the tolls on the Severn bridge - we will see the benefits of that only if this road is upgraded - but about the possibility of a major problem happening in the Brynglas Tunnels, which would effectively shut the M4 and close off one of Wales’ major pieces of infrastructure," the Conservative MP said.

"We need to have that alternative because the day will come when major work will have to be carried out in the Brynglas Tunnels, and if there is no M4 relief road there when that happens, the result could be absolutely devastating for the whole economy.

"I very much hope that the government in Wales get on with this."

Newport East MP Jessica Morden also spoke during the debate, which was led by former Welsh secretary Stephen Crabb, saying: "The M4 around Newport is a route of strategic importance and critical to the Welsh economy, but it is also an absolute nightmare for many of my constituents and businesses to navigate.

"If there are serious incidents - and there are, frequently - they bring our part of south Wales to a halt, causing misery for people trying to get to and from work, and resulting in a big cost to business.

"I have constituents, family members and friends, as well as colleagues working in my office, who commute, so I understand the cost all too well.

"The M4 motorway between Magor and Castleton does not meet modern motorway design standards, yet it carries a greater volume of traffic than it was designed for."

The Labour MP added she recognised the views of campaigners concerned about the environmental impact on the protected Gwent Levels and said, if the Assembly ultimately blocks the plan, much more investment would need to be put into public transport to relieve the predicted increase in traffic.

"People who regularly use the M4, and people who do not, want politicians to make an informed decision with all the facts at their disposal," she said.

"I do not envy Assembly Members that decision, but I know they will make it with integrity after careful consideration."

Torfaen MP Nick Thomas-Symonds also spoke during the debate, saying it is "imperative" a decision is made soon.

Speaking at the end of the debate, Mr Crabb said: "We are at a moment that requires a difficult and challenging decision from the Welsh Government, but my hope is that they will make the right decision in the interest of future generations of Welsh people."