The retirement of Concorde four years ago was greeted by many people like the passing of a much-loved celebrity. Moreover, it was a watershed, the passing of an age in which sheer, pointless glamour outweighed mere cost in transatlantic travel, the end of an era. Now, however, the glory days of supersonic flight may be about to be revived.

Last week at the Paris Air Show, concepts were being touted by aviation entrepreneurs and the sleek designs proposed by two companies generated great interest. Both, however, have rejected the Concorde dream of mass-transit supersonic flight and are pitched, instead, purely at the mega-rich.

Seating about a dozen people, the new supersonics will be capable of flying from London to Washington in four hours or from Seattle to Tokyo in five hours – at least a third less than current jets.

One of the entrepreneurs pushing to reintroduce supersonic travel is Michael Paulson, son of Allen Paulson, the founder of Gulfstream, the business-jet manufacturer. He is using a Lockheed Martin Skunk Works design called the Quiet Supersonic Transport (QSST). He hopes to achieve a first flight of the aircraft in 2013 and to start commercial sales by 2015. Developing the QSST will cost about $2.5 billion (£1.25 billion).

But in the race to return to supersonic travel, the QSST has a rival. Its competitor is being designed by Aerion, which was founded by Robert Bass, a Texas oilman.

Mr Paulson said: “Business aircraft have been in production now for nearly 50 years and haven’t progressed much in speed. The QSST will mean a quantum increase in productivity for the world’s leaders in commerce and government.”

However, there are two glaring problems with trying to develop supersonic jets for the 21st century. The first is environmental and the second is cost. At a time when the big aircraft manufacturers and airlines are pushing for more fuel-efficient and quieter planes, the idea of selling a supersonic jet could be controversial.

Doug McVitie, managing director of Arran Aerospace, said: “These aircraft are the opposite of green. They are putting their foot on the gas when they should be easing off. They are conspicuous consumption by the very richest in an era when most people are becoming more aware of their carbon dioxide emissions.”

The other environmental issue is noise, as anybody unlucky enough to live under Concorde’s flightpath will remember. QSST and Aerion insist that their designs will generate a much smaller sonic boom than either Concorde or a modern fighter jet.

Over inhabited areas and the continental United States, the aircraft will cruise at Mach 0.98 before accelerating past the speed of sound to Mach 1.6 over water or uninhabited areas.

Another concern for the supersonic business jet market will be the forecast $80 million price tag. However, the business jet sector is growing rapidly as executives try to limit the time they spend hanging around large airports waiting to clear security. According to the General Aviation Manufacturers’ Association, there were 885 business jets worth $16.5 billion delivered by companies such as Gulfstream and Bombardier last year.

Also, there are a number of high-worth individuals willing to spend more than $100 million to buy their own aircraft. One private buyer recently bought an Airbus A380 at a cost of $300 million. Supersonic travel would be cheap by comparison.

Elite air

Concorde

Length: 202ft

Max cruise speed: Mach 2 (1,350mph)

Seats: Up to 108

London to New York: 3hr

QSST

Length: 132ft

Max cruise speed: Mach 1.8

Seats: 12 to 14

London to New York: 3.5 to 4hr

Aerion

Length: 148ft

Max cruise speed: Mach 1.6

Seats: 8 to 12 L

ondon to NY: 3.5 to 4hr

Source: Database, company websites

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