Four larger Scharnhorsts would force a British capital-ship emergency

The counterfactual arrival of four larger Scharnhorst-type battleships in December 1939 would concentrate British strength at Scapa Flow and redirect imperial shipbuilding toward escorts.

Question

How would four upscaled Scharnhorst-type ships appearing in December 1939 affect the war?

Short answer

They would create a formidable fleet in being, force British concentration in home waters, and trigger an emergency expansion and redistribution of Allied shipbuilding.

Notes

Six fast German capital ships would be too strong for the Royal Navy to meet casually or in dispersed detachments. Britain would have to reconsider Mediterranean deployments and retain a powerful concentration at Scapa Flow in case the German force broke into the Atlantic. The ships' value as a fleet in being would reduce battleship escort available to convoys even before they sailed. Britain would accelerate every capital-ship and carrier program it could while shifting more corvette, frigate, and escort construction to Canadian, Australian, and Indian yards.