Under-used Southend airport is being positioned to relieve the capacity-constrained London area ahead of a new runway being built at Heathrow.

The Essex airport currently handles around one million passengers a year – fewer than a quarter of the numbers using London City airport – but the potential for growth and the strategic case for Southend is being highlighted at a time of limited south-east aviation capacity.

Glyn Jones, chief executive of Stobart Air and a former managing director of Luton airport, is pressing the case for Stobart Group’s Southend airport 45 miles east of the capital to become London’s fifth airport.

“We are a London airport, but we haven’t yet got that through to the customer,” he told The Times.

“We have a shorter journey from the plane to the City of London than Luton or Stansted and, depending on the trains, Gatwick. We are five minutes from the plane here to our own train station, 15 minutes if you have baggage in the hold, and there are six trains an hour to Liverpool Street.”

Jones has run the numbers from the Civil Aviation Authority and the Department for Transport to make his case.

London City, presently at 4.5 million, will be at its seven million capacity by 2021. Gatwick will be full next year, since it has a capacity of 45 million and is already at nearly 44 million.

Luton is going through a big reconstruction to get its limit up to 18 million; at 14.5 million now, it will be full by 2019.

Stansted has a capacity of 35 million, is only at 24 million but all its spare capacity is off-peak and Heathrow is full and its third runway probably will not open until 2030.

“The projections say all London’s airports will be full by 2021, except Southend,” Jones said.

“We have planning capacity for five million passengers a year, but with the capacity for 36 movements an hour we could easily get to ten million.

“We will do 1.1 million in 2017 and have said we will do 2.5 million in our financial year to March 2019. The nine million extra capacity here is the big opportunity. It is the strategic opportunity for London.”

Existing London market capacity is 162 million passengers, with an absolute maximum at the beginning of the 2020s of 190 million. The sums mean that a third of London passenger growth could come at Southend.

However, Southend is not capable of handling long-haul wide-body aircraft. The small 90-seat regional turboprops that would happily use it, and which Stobart Air itself operates in the livery of Aer Lingus Regional and Flybe, do not produce the passengers volumes.

Also Essex is already well-served by Stansted and the train connection from Southend into the City takes 53 minutes on elderly rolling stock.

The airport argues is that the rail connections will only get better. It already serves the Stratford Olympic Park transport hub will be linked into Crossrail within a couple of years.

Expansion of Southend, where easyJet bases just three aircraft, is the most capital-efficient of any London airport, it claims

The £200 million it aims to spend – some coming from the sale of Eddie Stobart Logistics – for ten million passengers works out at roughly £20 million per million passengers.

That compares to Heathrow’s £18 billion third runway which works out at £31 million per million passengers and London City’s £344 million expansion delivering only 2.5 million more passengers.

Jones also argues that airlines serving London are still looking to grow. British Airways is studying the development of non-Heathrow point-to-point routes, while Wizz Air is expanding at 20%.

Stobart is hoping that EasyJet will pull out of Ryanair-dominated Stansted and could redeploy as many as 20 aircraft at Southend while continuing to grow at Gatwick and Luton,

Jons said: “The airlines have got some strategic decisions to make, but for us we believe when the dam bursts, it bursts.”