A UK mandate requires an increasing share of the nation’s jet fuel to be provided by so-called Sustainable Aviation Fuels (SAF), rising from 2% in 2025 to 22% by 2040. But a new proposal threatens to undermine the policy’s sustainability goals.With its SAF Mandate, the UK became a leading international example by only allowing for biofuels made from residues and wastes (such as used cooking oil, agricultural residues and waste wood) and electro-fuels to count toward the target. However, under reported pressure from the biofuel industry and concerns about meeting the mandate’s goals, the U.K. Department for Transport published a call for evidence late last year on the possibility of using food and other non-edible crops to produce jet fuels.Allowing crop-based aviation fuels to count towards the mandate’s targets would be deeply problematic for people and the planet. WRI analysis shows that meeting the 2040 target through crop-based biofuels would require between 1.4 million and 1.6 million hectares of land, just to meet 22% of expected jet fuel demand. Allowing crop-based biofuels could also exacerbate deforestation, threaten food security and, ironically, emit even more greenhouse gases than continued use of fossil fuels — the exact opposite of what the U.K.’s SAF Mandate is intended to do.The U.K. government is expected to decide whether to introduce any change to its mandate by the end of this year. Here, we outline the many reasons why relaxing its feedstock eligibility rules would be a real step in the wrong direction.Crop-based Biofuels Exacerbate the Global Land Squeeze and Ecosystem ConversionDedicating land to biofuel production has large implications for food security, nature and the climate. Crop-based biofuels are produced with food crops like soy or corn, non-edible crops like grasses and fast-growing trees (called ‘energy crops’), and/or cover crops grown in between food harvests to protect the soil. Today, at least 32 million hectares of cropland are used globally for biofuel production — an area roughly the size of Poland, or the entire arable area of Ukraine.The rising use of land for energy adds to all the other growing demands on land. A WRI report found that demand for crops is likely to increase by 56% from 2010 to 2050, with demand for meat and milk rising by 70%. This would require 600 million hectares of new farmland — an area nearly twice the size of India — even if historical yield growth trends continue. Agricultural expansion is already a leading driver of deforestation and ecosystem degradation, and increases agriculture’s negative impacts on soil health, water quality and biodiversity.The U.K. is already an outsized contributor to the global land squeeze. Approximately 40% of the food consumed in the country is imported, and producing its main agricultural imports requires 13 million hectares of land. As a comparison, the total area of arable crops in the U.K. was only about 4 million hectares in 2025.Any use of food, animal feed and energy crops, grown in the U.K. or abroad, to produce aviation fuels for the U.K. market will only add to these demands by displacing food production and fuelling more ecosystem conversion to replace it. In other words, the amount of food or feed that was once produced on land that would be used for aviation fuels will need to be replaced by crops grown elsewhere to compensate for the lost supply — with negative impacts on nature and the climate.Meeting the U.K. SAF Mandate’s 2040 target with biofuels made from food crops (soybean, rapeseed and/or wheat) would require between 1.4 and 1.6 million hectares of farmland, equivalent to 35-39% of the current area of arable crops in the U.K. Biofuels made with non-edible energy crops such as grasses would require a similar amount of cropland. This enormous area is about 10 times larger than the amount of U.K. cropland dedicated to biofuel crops in 2024.Source: WRI calculationsCrop-Based Biofuels Threaten Food SecurityIncreasing the use of crops for aviation fuels would also undermine food security, one of the U.K. government’s priorities. Diverting cropland to produce fuels for airplanes is particularly problematic at a time when climate change, conflicts and geopolitical instability make the occurrence of food shortages and food price spikes increasingly likely.Research already shows that increasing crop-based biofuel demand leads to higher crop prices. For example, biodiesel demand for palm oil, soybean, rapeseed and sunflower oil increased global vegetable oil prices by an estimated 20% from 2002-2018.Feedstocks used to produce biofuels are globally traded. Their prices closely track each other around the world, as shown in the figure below. When demand for a biofuel crop feedstock rises in one country, prices rise by similar amounts for that same crop everywhere. This stimulates cropland expansion wherever it is most cost-effective — often in tropical forests, the preservation of which is essential for carbon storage, water provision, biodiversity protection and countless other ecosystem services.Using Crop-based Biofuels Would Increase EmissionsCrucially, such a large use of additional cropland would actually increase emissions more than continued use of fossil fuels for aviation. Global food demand continues to rise. If agricultural land is diverted to growing crops for biofuels, then food will need to be produced elsewhere, leading to conversion of carbon-storing forests and other natural ecosystems into farmland, thereby increasing greenhouse gas emissions. Once the emissions related to this indirect land use change are fully accounted for, research by WRI and others shows that using crop-based biofuels actually increases overall emissions, relative to only using conventional jet fuels made from fossil fuels. This would run directly counter to the SAF Mandate’s decarbonization goal.Using Non-Food Crops Grown on Degraded Land Is Also ProblematicOne of the arguments often used by advocates of crop-based biofuels is that energy (non-edible) crops can be grown on ‘marginal’ or ‘degraded’ land. The call for evidence specifically asks about this potential.The problem is that there is no accepted definition of what counts as marginal land, and its availability is often overestimated. What are often called ‘marginal lands’ are areas that are still actively managed, often for livestock production. Hence, using them to produce fuels would require producing animal feed elsewhere.Also, marginal land often provides a number of benefits in terms of biodiversity conservation and provision of ecosystem services like pollination. Even employing truly unused marginal land to produce energy crops for aviation fuels would incur trade-offs. For example, afforesting or rewilding degraded lands could produce more carbon benefits overall than using these lands for energy crops.In general, attempts at producing energy crops like jatropha or castor oil on low-quality soil have not been successful so far. The reality is that the biofuel industry is overwhelmingly reliant on food and feed crops like corn, wheat, soy and palm oil grown on prime agricultural land. Calls to shift production onto degraded land at a meaningful scale are wishful thinking at this point.The call for evidence also asks about the potential of cover crops to produce biofuels for aviation. Sometimes a second ‘cover’ crop is planted in the off-season to protect and improve the soil, without being harvested. It has been suggested that in some regions a biofuel crop could be planted as a cover crop and then harvested, but this, too, comes with its own complexities. For example, letting a cover crop mature to harvest may take longer and impinge on the main growing season, displacing food production by decreasing the yield of the primary crop. In addition, getting a harvestable yield from a cover crop can increase the need for chemical fertilizers, which come with their own set of environmental concerns.Using Biofuels for Aviation Would Not Actually Boost the U.K.’s Energy SecuritySome see the possibility of allowing production of jet fuels with food crops as a way to support U.K. bioethanol producers, whose interests have been impacted by the recent trade deal with the United States. The deal includes a duty-free quota for 1.4 billion liters of U.S. bioethanol, which was previously taxed at 19%. But this, too, is wishful thinking.U.S. bioethanol is 24% cheaper than bioethanol produced in the U.K. and represents a large share of imports into the U.K. for road transportation fuels. The U.S. industry for jet fuel made with bioethanol is also more advanced than in the U.K. In other words, it is very likely that allowing food crops would mostly benefit U.S. farmers and fuel producers rather than those in the U.K. and would not contribute to U.K. energy security.The same holds for aviation fuels from oily crops via HEFA (a different and more established pathway than the one used to produce aviation fuels from bioethanol). The U.S.’s production capacity is currently taking off. If aviation fuels are allowed to be produced with food in the U.K., aviation fuels produced via HEFA could be imported from the U.S., thereby benefitting U.S. farmers and biofuel producers rather than U.K. ones.The U.K. Should Continue to Provide Global Leadership on Aviation DecarbonizationIt’s important to consider the global context. The U.K. is currently a leader in aviation decarbonization. Along with the E.U. and China, the country does not allow crop-based biofuels to count toward regulatory targets.As the sixth-largest economy in the world, the U.K.’s actions matter both nationally and globally. If it decides to relax feedstock eligibility rules for biofuels for aviation, this may have important consequences elsewhere.In short, the U.K. got it right the first time. The evidence to support this decision has only become stronger and is not altered by the challenges faced by U.K. farmers and biofuel producers. The U.K. government should support farmers directly to sustainably produce food for people. Allowing food to be used for the aviation sector would only increase carbon dioxide emissions through a policy originally intended to reduce them.The country should retain its current policy to exclude food, animal feed, and energy crops for aviation fuels. It’s a policy that sets a positive example for the rest of the world and supports food security, healthy ecosystems and true decarbonization.