STARING into the terrifying thunderous tumult of the Corryvreckan whirlpool, it's easy to see why its sheer primal energy has fascinated people for centuries. Now Edinburgh folklorist Stuart McHardy has suggested a startling new theory - that the awe-inspiring natural vortex between the islands of Scarba and Jura in Argyll and Bute was the true origin of the Holy Grail. At its wildest, some say the whirlpool forms a spectacular swirling cauldron 300 feet wide and 100 feet deep. The cause is hidden beneath the waves – a giant rock pinnacle rising from the depths to within 95 feet of...