I cannot remember the details but assume it was Governmental pig headedness and union intractability ending up in outsourcing things. By selling off various industries.
It used to anger me back in the 70/80s that Constructional fabrication companies would buy Russian rolled steel sections instead of British steel sections. Russian Steel sections were far cheaper than British Steel ones.
As far as I know the quality was nearly the same BUT.
Regarding Shipbuilding the Tyne was just too narrow to build big ships and nobody would invest the money to say build a big construction dock say at Jarrow slack or Tyne Dock.
What was never taken into account was the knock on effect of closures. For every shipyard worker there was probably another person employed in shops and companies to feed and clothe them.
If a company moved overseas was one job lost or 5 jobs or more!
Allan C.