The government is forced to sell steel at a loss, because all the buyers for whom this is a such a vital supply would otherwise buy cheaper imported steel, every single one of them.
And ultimately all the ore and coke used to make the steel are imported anyway.
2 things: a) Government plays a part in the cost of things - especially years of mis-investment around energy generation has sent British prices to the stratosphere and employment taxation levels greater than those 'cheaper' producers. b) The 'cheaper' producers are still _producers_ and thus have control - if they need to hoard their own supply they will, or if they need to leverage it for some political gain they might.
The same is, as far as I can grasp it, true for butter, bread, milk and eggs. Only there, it is already established.
Until something happens that disrupts the supply chains from abroad and suddenly there's an issue