POSTER companies in America have airbrushed a cigarette from the hand of PaulMcCartney on the Beatles' Abbey Road album cover. They have performed this Leninist gesture in response to the anti-smoking lobby. In the late Sixties, the cigarette in question played a key role in a widely held conspiracy theory concerning the death of PaulMcCartney. The rumour was rife that McCartney had died in a car crash, and had been replaced by a lookalike. On the cover of Abbey Road, "Paul" is barefoot (corpses are often buried without shoes), and his eyes are closed, as if dead. He is also out of step with the rest. The other Beatles are wearing tell-tale clothing: Ringo, dressed in black, is the pallbearer, George, in denim, is the gravedigger, and John, all in white, is the preacher. Behind them is a Volkswagen with the number plate "28 IF", signifying that Paul would have been 28 years old if he had lived. Furthermore - and this is where this week's news comes in - the lookalikePaul is holding his cigarette in his right hand, whereas every Beatles fan knows that the real Paul is left-handed. Spooky, indeed. It is quite a while - at least 25 years, in fact - since I last heard anyone repeating this great mound of evidence with a furrowed brow and a straight face. But with repetition, the list becomes peculiarly convincing. One can only hope that the air-brushing of Paul's cigarette by a person or persons unknown ignites afresh all the old conspiracy theories. Since the claims concern a celebrity, it can be only a matter of days before a 12-man police squad bursts into Sir PaulMcCartney's home to ask him whether or not he is real. If he hesitates for even one second, he will be bundled off to the nearest police station, where he will be asked to run through the words of "Love Me Do" without hesitation, repetition or deviation. The police must get to the bottom of this great mystery for once and for all. If Sir Paul isn't Sir Paul, then who on earth is he? Tommy Steele? And how many others among our best-loved celebrities are being played by sinister impostors? Soon after the death of HM the Queen Mother, I noticed that "Sir Paul" began to take on her appearance. What does it all mean? Is the impostor making a bid for the Royal status? Alone among columnists, I am often hit by the feeling that I really don't know what to believe any more.