Unfortunately you can't really rely on this sort of comparison between numbers obtained from different sources, except in the most unambiguous circumstances, which rarely arise for a complex topic such as sector emissions and cost of mitigation. The 1.5% and 2.4% figures may use different methodologies. The total-cost-to-decarbonize estimate probably entails a variety of unrealistic assumptions; it's hard to take into account future improvements in technology, all of the different ways the market will find to minimize costs, etc.
FWIW from the same gov source
"The blast furnace route forms the majority of UK and global steel production. In
2018, 82% of UK steel (5.9 million tonnes) was produced using the blast furnace
route at Tata Steel’s Port Talbot site and British Steel’s Scunthorpe site. The
Government estimated that 95% of iron and steel industry emissions (and
around 15% of total industrial emissions) come from the Scunthorpe and Port
Talbot blast furnace sites."
It does not differentiate between the two, though.
If you're interested, I discuss the general danger of working with such quick-grab numbers in https://climateer.substack.com/p/numbers.