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The Department for Transport (DfT) announced the review in its latest Low Carbon Fuels Updates on Tuesday June 16, saying it had received feedback from industry sources that supplies of advanced non-hydroprocessed esters and fatty acids (HEFA) fuels and power-to-liquid (PtL) fuels could be lower than previously anticipated once new SAF mandate requirements take effect from 2027 and 2028.
The move comes less than 18 months after the UK’s SAF mandate entered into force on January 1, 2025. The mandate requires fuel suppliers to increase SAF blending over time, while a dedicated PtL obligation will begin in 2028.
The government stressed that it is not seeking to reduce the overall mandate targets or weaken the framework’s environmental ambition. Instead, it is seeking evidence on how best to ensure future compliance while maintaining investor confidence and supporting the development of a domestic SAF industry.
“We will not propose any changes unless there is a strong rationale,” the DfT said, adding that any future amendments would be subject to a separate formal consultation process.
While the DfT said there were encouraging signs regarding near-term HEFA availability, it highlighted growing concerns about longer-term reliance on a single production pathway.
From 2027, a HEFA cap will begin limiting the proportion of mandate compliance that can be met through HEFA fuels produced from feedstocks such as used cooking oil (UCO) and animal fats.
The policy is intended to encourage investment in alternative pathways, including alcohol-to-jet (AtJ), synthetic SAF (eSAF) and other advanced technologies.
The DfT noted that future HEFA supply is expected to face increasing pressure as more countries introduce SAF mandates and competition for feedstocks intensifies across the transport sector.
The government also warned that insufficient availability of advanced fuels could leave suppliers increasingly reliant on buyout payments to meet compliance requirements.
While buyouts cap compliance costs and can signal unmet demand to investors, they do not deliver the emissions reductions that the SAF mandate is designed to achieve.
According to the DfT, non-HEFA fuels will account for only 7.7% of total mandated SAF volumes in 2027, meaning most compliance can still be achieved through HEFA in the early years of the cap.
The department said, however, that long-term aviation decarbonization would require a broader mix of technologies and feedstocks.
The call for evidence also seeks industry views on potential flexibility measures, including increasing the proportion of certificates that can be carried over from previous years, extending certificate validity periods and introducing additional incentives for advanced fuels.
In parallel, the government is seeking updated evidence on fuel tankering, where airlines carry additional fuel from one airport to avoid purchasing fuel elsewhere. The DfT said the practice could undermine emissions reductions because carrying extra fuel increases aircraft weight and fuel consumption.
Alongside the review, the government announced a new Low Carbon Fuels Fund, which will provide up to £219 ($289) million between 2026-27 and 2029-30 to support low-carbon fuel projects. The program follows previous government support delivered through the Advanced Fuels Fund and is expected to complement the UK’s planned Revenue Certainty Mechanism for SAF projects.
The policy review comes as official data continues to show a SAF market heavily dependent on HEFA production.
According to the DfT’s fourth provisional SAF dataset, UK-produced SAF volumes reached 370 million liters in 2025, equivalent to 2.49% of total aviation fuel supplied. Total aviation fuel demand reached 14.713 billion liters during the year, with fossil jet fuel still accounting for 97.51% of the fuel pool.
All SAF supplied under the current dataset was produced through conventional bio-based pathways, while no PtL volumes were reported ahead of the dedicated PtL obligation beginning in 2028.
Feedstock data showed that all SAF volumes recorded under the UK’s certificate framework originated from UCO. Of the 158.74 million liters recorded under the voluntary certification system, approximately 85% originated from China, highlighting the market’s continued dependence on imported waste-based feedstocks.
The DfT also reported that 175 million SAF certificates were issued during 2025, all linked to HEFA production pathways.
The concentration of supply reflects a wider challenge facing the SAF sector as blending requirements increase. Under the UK mandate, SAF obligations will rise from 2% in 2025 to 10% by 2030 and 22% by 2040. A dedicated PtL target will begin at 0.2% of jet fuel demand in 2028 before increasing to 3.5% by 2040.
Industry participants have increasingly raised concerns about the long-term scalability of HEFA production.
Sources have told Fastmarkets that producers, airlines and policymakers are paying growing attention to alternative pathways, including AtJ, methanol-to-jet and eSAF technologies, amid concerns over the future availability of waste-based feedstocks such as UCO and tallow.
Several sources said current SAF availability in Europe remains sufficient to meet existing mandate requirements; however, concerns are increasingly focused on the second half of the decade, when higher blending targets, HEFA caps and dedicated synthetic fuel obligations are expected to increase demand for alternative pathways.
Market participants have also pointed to the unusually narrow spread between SAF and hydrotreated vegetable oil (HVO) in recent months as evidence of growing competition for the same pool of waste-based feedstocks.
Sources said this dynamic has further strengthened interest in technologies that are less dependent on UCO availability.
The call for evidence will remain open until July 28, with the government intending to publish a summary of responses and next steps later this year.