It's not being built for fuel security.
It's for coke in virgin steel making. Carbon is essential in the steel making process (steel is iron + carbon + other additions to get different properties). At present the coke for our steel making is mostly imported from Canada, which is obviously massively less green than having a domestic supply.
The UK is still on track to close down all coal fired power stations in the UK by October 2024.
We do need to retain a domestic steel supply too btw. It's the basis for all infrastructure in pretty much everything. We would be the only developed nation without a domestic steel supply if we let it go, and completely at the mercy of China. We're all seeing how well that's going at the moment for gas with Russia.
Oh, and the steel industry will need to be decarbonised as part of meeting net zero 2050 (coke as an ingredient is essential and not part of decarbonisation as the carbon is retained in the steel, so not polluting). This probably mean using hydrogen as fuel for blast furnaces etc rather than natural gas. (Menntioned before some suggests shutting down steel to be green)