This article in the Spectator sounds right

Of course EU competition law kicks in too

The government needs to examine how much British Steel products are used in our defence and security sector

The import of cheap steel – especially from China – is a major economic reality. Nevertheless should the UK rely on that source.

https://blogs.spectator.co.uk/2019/05/the-eus-role-in-the-demise-of-british-steel/