Theresa May’s attempt to rebalance the UK economy risks being derailed without a transport revolution to modernise links to the north of England’s airports, business leaders have warned, reports The Guardian.

An independent commission found that the north of England had capacity for an extra 60 million air passengers but was being held back by outdated road and rail links.

John Cridland, the chair of Transport for the North, who led the study, said: “These inadequate ground transport links, coupled with not enough direct services to key international destinations, mean that passengers from the north often have to travel from southern gateways. They also act as a disincentive for both business and leisure travellers to visit the region.”

The business leaders behind the report, the Independent International Connectivity Commission (IICC), warned that “business as usual would simply not be good enough for the north to meet the ambitions of economic rebalancing” set out by the prime minister.

The report said the north of England was missing out on billions of pounds of growth and potentially thousands of jobs due to poor transport connections to its regions airports and ports.

The report found that while the north currently accounts for around 25 per cent of the UK’s population, its seven airports handle just 15 per cent of all airport passengers in the UK “suggesting a degree of underperformance in the connectivity provided”.

It said the number of air passengers in the north could nearly double to 75 million by 2050 with modernised road and rail links and new international destinations from airports such as Manchester, which is the biggest outside London.

The commission recommended that by 2050 90% of long-haul passengers should be able to fly directly from the north to their international destination, compared with just 50% currently.

Cridland said: “It’s clear that the north’s ports and airports are key economic assets for the region, with nearly 40 million passengers flying from the region each year and around a third of all UK freight using northern ports.

“Yet we know that the lack of access to and from our ports and airports is holding them back, with congestion on our roads and railways making it difficult for people and goods to reach international gateways.”

He added: “Unlike in the south, where ports and airports are heavily congested, the north’s international gateways have unused capacity. We believe international connectivity starts on the ground; by properly utilising available resources we can both boost the economy of the north and ease pressure on overloaded ports and airports elsewhere. We need to start promoting the north as a destination of choice, both to do business and to visit.”

The report echoes concerns expressed by Ken O’Toole, the chief executive of Manchester airport, who told the Guardian in September that there was an “overemphasis on the south-east at the expense of everywhere else” in the government’s aviation policy.

O’Toole said in response to the IICC report: “The commission has confirmed what we have been saying for some time – that large-scale investment in road and rail infrastructure is needed to ensure all parts of the north are connected to its primary global gateway. It is this combination of world-class domestic and international connectivity that is needed to ensure the goals of the northern powerhouse independent economic review and the UK’s new industrial strategy are realised.

“That is why government must seize the opportunity presented by the creation of a new aviation strategy to act on the recommendations of this report and and deliver the appropriate policy to enable UK airports to secure as many connections with global markets as possible. As well as investment in transport infrastructure, that includes reform of aviation taxes and border and visa policies that encourage, rather than hinder trade and tourism.”

The report comes as George Osborne prepares to publish the first work by the Northern Powerhouse Partnership he launched in September after he was sacked by May when she became prime minister.

It is understood Osborne’s report, due to be published on Friday, will have transport and global connectivity as a central pillar, along with issues like skills and digital infrastructure.

His report is also set to give backing to plans to boost east-west connectivity by government investment in northern powerhouse rail, as well as emphasising the importance of airports to economic travel.

Osborne said: “I created Transport for the North in 2015 because it was clear to me the role that transport connectivity would play in delivering a northern powerhouse. Much has been said about the importance of connecting together the great cities of the north but today’s report demonstrates how vital it is that the region also has strong links to the world.

“In the years to come, the great airports and ports of the north will play an increasingly important role in driving greater levels of investment, trade and tourism into the UK and every effort must be made to ensure that they continue to grow and it is as easy as possible for passengers to access these key national assets.

“Since the Northern Powerhouse Partnership was created last autumn, I have spoken to hundreds of businesses, civic leaders and other organisations across the north and their feedback has been uncompromising – transport connectivity will always be the lifeblood of the region’s economy.”