Roadchef claims plans for a relief road for the M4 in South Wales could jeopardise the future of its Magor motorway service area and damage road safety.

The company says it supports the delivery of an M4 relief road, but the proposed route means Magor Services at junction 23A, which has more than two million visitors a year, will no longer be on the motorway.

Drivers would be required to undertake a two-mile diversion to access Magor Services under the plans, and it says independent research it commissioned shows 68% of drivers would be less likely to use Magor Services if they were required to undertake such a diversion.

And while Department for Transport guidelines recommend a maximum distance between motorway service areas, it says this would leave a much longer gap.

In written evidence to an inquiry into the plans, Mike Axon, on behalf of Roadchef, claimed if people failed to leave the motorway due to the detour, the 16-mile (25km) gap between service stations, between Cardiff Gate and Magor, would become a 49-mile (78km) gap, with motorists having to travel to Leigh Delamere services.

He said it would create one of the “longest distances and times between stop rests on the UK’s motorway network”.

“We fear this will lead to a loss of trade at Magor, risking the 190 jobs at the site.”

Roadchef is in dialogue with the Welsh Government to identify how J23A could be reconfigured to keep Magor Services on the M4.

Roadchef chief executive Simon Turl said the lack of directly accessible services at the side of the motorway would “significantly increase the risk of major accidents due to driver fatigue”.

He added: “The absence of proper toilet and rest facilities for travellers using the newly-built motorway access route into Wales should and would raise serious questions for all of those responsible for its construction.

“The spectre of desperate road users relieving themselves along the hard shoulder of the newest motorway in the UK would be highly embarrassing and extremely dangerous.”

Speaking at the public inquiry in Newport, Rhodri Price Lewis QC, on behalf of Roadchef, said there was “overwhelming” evidence the current route would have a “significant accident risk”.

He said an independent road safety audit found access arrangements to the services could result in crashes as people navigated junctions and took comfort breaks at the side of the road.

He added that a westbound on slip road, costing £14.45m, should be built to stop motorists taking the risk of driving when tired.

In a written rebuttal, the Welsh Government said, while some road users “may be deterred” from using the services, “the reasonable road user with a compelling need to stop can and will be able to safely do so”.

Roadchef’s objections were, therefore, “matters of commercial impact rather than road safety”

It added creating an on slip road would delay building work on the relief road and would cost more.