If a decision on this has to be made by the end of this year, as BAE Systems boss is now saying, Whitehall has a tricky decision: allow Portsmouth to close, risking the Royal Navy being left with no domestic shipbuilding capacity, or cut the workforce and perhaps a yard on the Clyde, and hand Scottish nationalists a substantial campaigning gift.

BBC: Shipyards on the slipway

One Royal Navy captain after another would champion his new command's inaugural performance at sea trials, or praise the yard to the hilt when a vessel returned to the port of its birth.

BBC: Reliving Swan Hunter's darkest day 20 years ago