The ASA probe was triggered by just five complaints about the advert, which aired over radio and featured a voice saying that Virgin was bidding “to become the world’s first commercial airline to fly transatlantic on 100pc sustainable aviation fuel”.
Mark Harper, the then transport secretary, accompanied Sir Richard aboard the experimental journey, which was the result of a government competition to receive £1m of funding for the first net zero flight between London and New York.
About 90pc of the SAF used for the flight came from recovered animal fats, with the rest refined from sugars derived from industrial corn starch.
Since the carbon produced had been recently captured from the atmosphere, that delivered a lifecycle CO2 saving of 64pc.
The ASA said Virgin’s reference to the flight being “100pc sustainable” and “sustainable” was therefore misleading.
Miles Lockwood, the ASA’s director of complaints and investigations, warned that companies must produce “robust evidence” when making such claims.
Virgin Atlantic said the advert’s wording mirrored that used by the Department for Transport in launching the competition and was intended to reference the type of fuel used, rather than implying that SAF in itself was 100pc sustainable.
A Virgin spokesman said: “SAF is a term used globally by industry and government for fossil-alternative aviation fuels that adhere to specific sustainability criteria.”
It added that the advert accurately stated that the flight “would be operated as a single, non-commercial flight using 100pc SAF”.
The ASA ruling calls into question the ability of airlines to promote their investment in efforts to reduce carbon emissions.
The International Air Transport Association, which represents more than 300 carriers, said that while it is right that sustainability claims should be scrutinised, the industry must not be prevented from communicating its strategy for reducing emissions.
A spokesman said: “Meeting the net zero target will rely heavily on SAF. That is why raising awareness about SAF through communication is vital.”