“It works!” declares Virgin Atlantic founder Sir Richard Branson as we cross the Atlantic on this record-breaking flight using 100% sustainable aviation fuel (SAF), largely made up of used cooking oil.

In his affable way, he recalls the times he had to be rescued from the very same ocean during previous record-breaking attempts. We smile along, a little nervously.

There are no ordinary passengers on board the Boeing 787. Instead, milling about the cabin are engineers, scientists, aviation officials, Mark Harper, the transport secretary, and journalists.

So what’s it like to travel on the “fat flyer” as it’s been dubbed?

Well, perhaps a little disappointingly, just like any other flight.

SAF looks, smells and performs just like normal aviation fuel and can be dropped in normal engines without the need for modification.

Sir Richard and Virgin know how to make a big noise about their achievements so, as I look out of the window over the ocean, I ponder is this just another great way to get attention, or actually another important step along the flightpath to what the government likes to call “guilt free flying”?

The truth is, probably a bit of both.

Virgin Atlantic has, like British Airways and other UK-based airlines, genuinely committed to trying to find a greener, cleaner way of flying.

After all, in a highly competitive market they know passengers are demanding it.

Virgin points out it has one of the youngest and most fuel-efficient fleets in the skies which has already reduced carbon emissions by more than 20%.

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The airline is working hard to reach the government’s ambitious target to increase the use of SAF to at least 10% by 2030.

This flight however is not 100% emission-free, but rather “net zero” with the airline offsetting carbon emissions made during the journey.

Plus the very process of making SAF uses lots of energy, and SAF critics argue there simply isn’t anything like enough raw material or “feedstock” in the UK to produce it.

The Royal Society estimates more than half of all the UK’s agricultural land would be needed to produce enough SAF to replace the jet fuel used by Britain’s aviation sector.

Pressure is being put on the government to help invest in SAF technology and to scale up production.

Green campaigners also point to the growth in flying.

The International Air Transport Association expects the number of passengers to nearly double by 2036, and many environmentalists say the best way to save the planet is to drastically reduce our air miles.

So as flight VS100 ploughs along over the pond don’t be mistaken into thinking it is the answer to all our climate-friendly flying prayers.

Instead, SAF is a mid-term solution to helping make a decent dent in decarbonising aviation while other greener technologies, like hydrogen, are developed.