The RAF is "ready" to use green aviation fuels more if they are "readily available", the Chief of the Air Staff has said.
When asked why the RAF isn't using eco-friendly fuels as much as other air forces, Air Chief Marshal Sir Mike Wigston told Forces News "we're going as fast as the global sustainable fuel production industry is making it".
"I've already cleared our aircraft for a 50% blend of sustainable aviation fuel which is waste oil, chip fat, all sorts of oil, that has been recycled.
"And some of our aircraft will be cleared to [use] 100% sustainable fuel.
"The challenge is around the world, there isn't the production capacity to cope with the demand.
"But we're ready and we will use it, and would use it if it was readily available."
His comments come a week after the RAF's VIP Voyager aircraft achieved a "historic first" as it flew the Prince of Wales and Duchess of Cornwall to Jordan using sustainable aviation fuel which is said to be able to cut carbon emissions by up to 80%.
While earlier this month a Royal Air Force test pilot made history with the world's first-ever flight on 100% synthetic fuel.
Speaking about how the RAF can achieve net-zero carbon emissions, ACM Wigston said how aircraft are fuelled is the biggest hurdle.
Watch: RAF test pilot's world record flight on 100% synthetic fuel.
"It's easy to say we have a net-zero ambition but then when you stop and think about what we're going to have to do, it is pretty daunting.
"The most significant thing we are going to have to change is aviation fuel and the activity around flying because that by far and away is our largest sustainability impact. About 75% of my carbon footprint is around burning aviation fuel.
"There's a number of work strands under way – from looking at powering aircraft in different ways, with electric power or hydrogen power, to changing the way we make our fuels and making the fuels in a sustainable way."
ACM Wigston added there is also a focus on making RAF bases as sustainable as possible and "potentially as a source of renewable energy".
"We've got to start making the plans now because, otherwise, we will run out of time [to become carbon neutral by 2040], " ACM Wigston said.
"This is really complex, it's going to take many years to resolve and the time is now to get on with it."
Defence, including the RAF, is making a number of changes to improve its sustainability as the UK works to be carbon net-zero by 2050.