I've just been reading Stephanie Flanders' blog on the BBC news website; she's the BBC's economics editor.
Her argument today, and it's a strong one, is that the Great Depression of the 1930's was not caused by protectionism, and that Peter Mandleson has got it completely wrong ( Mandelson warns on protectionism ).
She quotes economist Milton Friedman, and ex Federal Reserve chairman Ben Bernanke, who say that the Great Depression was casued by the Federal Reserve when it failed to inject cash into the banking system after the crash in 1929. She also refers to the Gold Standard, where currencies were fixed to the price of gold, a sort of early version of the ERM and about as successful. Those countries who abandoned the Gold Standard were the first to come out of the Depression.
So, protectionism per se is unlikely to cause a depression. What it would do is make "Peter's Friends", the globalized multi-national corporations, suffer. They gain their power and (malign) influence from the scale of their operations, and you don't easily get that scale of operation when governements control the flow of capital, and insist on their own industrial strategy.
Peter's Friends must be looking aghast at the strength of feeling coming from the strikes surrounding Lindsey Oil Refinery. If that feeling gets attached to a political bandwagon, who knows where it will end. And in the end, maybe that wouldn't be such a bad thing.