Regular viewers of Channel 4's Mock the Week tap into a rich vein of humour from some of the sharpest knives in the comedy drawer, including the presenter, Dara O'Briain, Andy Parsons and the young pretender Russell Howard. But one of the keenest blades is Frankie Boyle, the caustic one with the spectacles. So it was with high hopes that I went to see the scathing Scotsman on the Midlands leg of his first national tour.