In a few months, Francis Urquhart will take his place in the history books as the longest-serving Prime Minister in this century. And yet - the country appears to be tiring of him. The movement to force him from power is gathering irresistible momentum. But F.U. is not ready to retire, still less to be driven from office. If the public are demanding new blood, then that is precisely what he will give them - the blood of critics, Cabinet rivals, any man or woman who stands in his way.