While aviation accounts for about 2.5pc of carbon emissions, flying is still limited to a relatively small proportion of the global population and the industry is under pressure to move towards zero emissions by 2050.

Step two is to move to greener fuels for existing engines. These will start off as biofuels but to make them greener synthetic fuels will be used. “E-fuels” will be made using electricity from renewable sources to generate hydrogen, which will itself be bonded to carbon dioxide to produce aviation fuel.

This fuel can be used in engines with a few modifications, mainly ensuring the seals still work with the new fuel, and Rolls hopes to have both existing and new engines using these new fuels by 2030. As well as recycling carbon dioxide, the synthetic fuel produces fewer particles that are blamed for helping warm the earth.

Along the way, airlines will seek to make shorter, more efficient routes rather than the dog-leg path they sometimes take today, and to reduce contrails, considered another warming factor as the soot combines with ice to absorb heat from the planet.

The third step is the new technology the company is now developing, including its new generator. Strapped to a jet engine it can supply more than 800 amps of current at 3,000 volts AC, hence the inches-thick cables.

The idea is to act as a stepping stone technology, much like the hybrid of the car world.

Rolls evisions a plug-in electric plane that can operate on battery power for some of the journey and then turn to fuel for the rest.

As with cars, the sheer weight of batteries poses a challenge for aviation. And for a machine aiming to defeat gravity, this is a problem nearly summarised by Newby. “If I take kerosene as my reference point, weight for weight, hydrogen is three times better, batteries are 60 times worse,” he says. “That’s the challenge for batteries.”

To put that in context, a long-range plane such as an A380 might have about a third of its weight taken up by kerosene-based jet fuel.

“Fundamentally that’s the challenge. So that’s why you will see all electric solutions at a smaller, shorter range at the moment. But what you can do is enhance that with some kind of hybrid solution.”