The UK’s new legally-binding mandate for use of sustainable aviation fuel (SAF) will take effect in a little over a month on January 1. Under legislation introduced in July by the country’s Labour government, 2% of all aircraft fuel delivered to operators at UK airports will need to be SAF from 2025, with this increasing to 10% in 2030 and then 22% in 2040.

According to the government, it will not increase the mandate above 22% until “there is greater certainty regarding SAF supply.” The legislation, which is based on a consultation conducted in 2023, also includes a requirement for the use of power-to-liquid fuels to increase progressively from 2028 to account for 3.5% of aircraft fuel by 2040.

The UK mandate includes a buyout mechanism intended to induce energy companies to boost SAF production or carry some of the cost of inflated fuel prices. Per liter prices for these will be set at £4.70 ($5.92) and £5 ($6.30) for standard SAF and power-to-liquid fuel, respectively.

This legislation also seeks to limit the feedstocks used in the hydroprocessed esters and fatty acids (HEFA) process used to produce SAF. However, the government said this requirement will not go into full force “until other types of SAF are commercially viable.” For the first two years, HEFA supplies will not be limited under the mandate, before being required to fall to 71% of total supply in 2030 and 35% in 2040.

The UK mandate starts out matching the European Union’s requirements, which also take effect at 2% from January 1. However, the EU mandate calls for SAF supplies to account for 34% of all aircraft fuel by 2040, and then rise to 42% in 2045 and 70% in 2050.

The UK government has included what it calls a revenue certainty mechanism in its mandate to encourage energy companies to increase SAF production capacity. It said its intention is to reduce investment risk and encourage producers to add new facilities in the UK, creating jobs in the process.