“At the moment there’s a lot of hydrogen hype,” says Matt Finch, UK policy director of campaign group Transport and Environment.

“A lot of people are saying ‘we can use hydrogen, we need hydrogen’. You hear it for cars, for trucks, for ships, for planes, for home heating, for chemicals.

“At the moment the UK effectively produces zero green hydrogen. To fulfil all the needs everyone wants is absolutely impossible.”

Mr Finch believes this means supplies of green hydrogen will probably have to be rationed for decades to come, and he says aviation may not be a priority for governments.

All of this means it is likely to be decades before zero-emission hydrogen planes become an everyday reality.

Even then, they are likely to be confined to short haul markets, at least to begin with. On long haul routes, synthetic sustainable fuels are widely expected to offer a more practical solution.

Nevertheless, these first tests on Salisbury Plain may one day be seen as the first, tentative steps towards a technological revolution in the industry.