Despite last week’s cautionary column about special supermarket offers which are often not so special, it will come as no surprise that a couple of days ago I succumbed to a “special offer”. There are mitigating circumstances however, for the item in question was what author Bill Bryson called “A British masterpiece”. He was referring to a biscuit to which I am rather partial — the Dark Chocolate Digestive. I’m afraid all dietary constraints go out of the window when faced with a chocolate digestive, but it has to be dark, not milk chocolate which does not appeal at all. Anyway I could not res…