The £400m Highways England upgrade – the biggest road building project in the north of England – means there are now motorway links all the way between Newcastle and London.

The extra capacity which comes from adding an extra lane in each direction near Catterick promises to reduce journey times by a fifth, and with safety benefits leading to less accidents, it is predicted to pump more than £1billion in the economy.

Over the next 60 years the improved road is predicted to prevent 450 accidents and save 20 lives.

The upgrade is part of the government’s £15 billion roads investment strategy, which is transforming the road network and improving connections between cities.

Secretary of State for Transport Chris Grayling said: "Our record investment to improve our roads is making a real difference to people’s lives – providing quicker and safer journeys for millions of drivers.

"This scheme will not only save motorists time stuck in traffic, but will also help unlock £1 billion into the economy.

"It also fills in the missing link to provide motorway-standard roads between Newcastle and London, helping businesses in the north by opening up new opportunities thanks to better and more reliable connections to the rest of the country."

Highways England Senior Project Manager Tom Howard said: "This is great news for the almost 70,000 drivers who already use this section every day and whose journeys will be safer and faster.

"At the same time we’ve also made it easier for local people to access the A1 safely, and we’ve planted miles of hedgerows and acres of woodland.

"This has been the biggest road project in the north and I would like to thank everybody involved in the scheme for their hard work and commitment in making it happen."

A total 13 miles of the route between Leeming and Barton has been upgraded to motorway standard, with an extra lane added in each direction. It means drivers using the M1 and A1(M) can have motorway standard journeys between Newcastle and London.

The upgrade has made access to the motorway safer via a new junction at Catterick and an improved junction at Scotch Corner.

The improvements also include 11 miles of new local access road, improving safety for local traffic and the surrounding communities as well as providing an improved route for cyclists, equestrians and pedestrians. There are also 10 new bridges to help people more easily get from one side to the other.

The project created more than 800 jobs, with 11 apprentices and 15 graduates recruited to the scheme.

To benefit the local environment 28 hectares of new woodland have been established and 18 miles of new hedgerows have been planted.

The improvements will translate into huge benefits for the economy.

David Laws, Chief Executive at Leeds Bradford Airport, said: "The A1 Leeming to Barton scheme will help to play a big part in improving surface access connectivity to Leeds Bradford Airport and this upgrade will ensure the economic benefits the airport can deliver for the wider Leeds City Region will be accelerated."

Contractors for Highways England will still be on the site over the next few weeks while they complete minor work such as landscaping.