As political dramas go, they just don't come any better than this - and Ian Richardson proves a master as an epitome of an ambitious schemer that even Machiavelli would have been proud of. He is "Urquhart", the chief whip of a government under new leadership. It's "Collingwood" (David Lyon) who takes the top job, but when he decides against promoting this local secret-keeper, he makes quite a mistake. Fuelled by his conceivably even more ambitious wife "Elizabeth" (Diane Fletcher) and taking advantage of the naive and malleable young journalist "Mattie" (Susannah Harker) he starts on a…