1938 import figures (from Britain's War Machine) are 1.3 million tons from Tunis, 1.3 million from Algeria, 0.3 million from France, 1.3 million from Sweden, 0.6 million from Norway and 0.4 million tonnes from other sources "not impeded by Germany" in OTL. Essentially ITTL the UK may lose 300,000 tonnes a year of French ore and some or most of the 500,000 tonnes of manufactured iron and steel products they imported from France and Belgium, but they're otherwise pretty much completely unaffected by the Germans due to holding Narvik and France remaining in the war.
It isn't just the blast furnaces which benefit though - the UK is saving a metric ****load of shipping which can go to Norway or North Africa in relatively small convoys rather than having to wait for big convoys to cross the Atlantic to New York, at which point they had to pick up steel or manufactured goods to save on shipping space. That's one of the major reasons the UK is - so far - not seriously affected by the absence of lend-lease and the relative lack of contracts with the US: their prewar supply chains are in a vastly better position. The main things they're missing are finished Iron & Steel products (which realistically would have been hit hard by the war in any case), Butter, Bacon and Eggs - the latter three having largely been imported from Denmark and Holland before the war. Butter can be substituted, but bacon and eggs are likely to be in short supply for the duration.