Decarbonization of all sectors is needed to mitigate the impacts of climate change. To accomplish this, hydrogen use has been suggested in many industries that currently rely on fossil fuels. Yet, the emissions intensity of hydrogen depends on how it is produced and distributed. Additionally, it is unclear whether hydrogen use leads to a reduction in GHG emissions compared to alternative decarbonization options such as electrification with renewables. Here, we systematically compare the decarbonisation potential of supplying hydrogen to the United Kingdom from a wide range of global supply chains. We do this by assessing 37,000 configurations of the hydrogen supply chain from primary energy production through to end-use. We find that imports of green hydrogen production are unlikely to be compatible with the UK Low Carbon Hydrogen Standard. The maximum mitigation potential is achieved when electrification is prioritized, and hydrogen used only for applications where electrification is not viable. This leads to a reduction of up to 280 Mt CO(2)e/a across all sectors considered in the UK. In the short term, use of domestic green hydrogen infrastructure should focus on displacing existing gray hydrogen use.