Carson has been, and is, Jekyll and Hyde. His public persona is the perky joker with the cackling giggle, as epitomised during his stint as a team captain on Question of Sport. But there is a dark side to the clown, which manifests itself in almost savage moodiness and sharpness.
At the moment, though, the smile is there. The job is going exceptionally well; he already has a Classic under his belt this season - Mehthaaf's win in the Irish 1,000 Guineas - and his mounts in this week's Epsom Derby and Oaks, Erhaab and Bulaxie, are vying for favouritism.
Carson has ridden 16 English Classic winners, including Derby heroes Troy, Henbit and Nashwan. He has been champion jockey five times, and his career total of 3,579 domestic winners has been bettered only by Sir Gordon Richards and Lester Piggott. He is, like most top jockeys these days, a millionaire; he lives in a large, luxurious house in the Cotswolds next to his own stud farm, he has a Mercedes and a private plane. He will be 52 this year, but he goes on.
He is still a driven man at an age when others have long since been content to hang up their boots in favour of a less gruelling way of earning a living. But while glory beckons, Carson, who thrives in the harsh glare of the limelight, will postpone thoughts of retirement.
It will come, though, and the jockey himself acknowledges sooner rather than later. He said: 'I honestly don't know when, but it is just around the corner. I haven't got to the corner yet, and I'm not even sure which one it is, but I'll know when I get there. I'm 51, and naturally I know I can't keep going for ever.'
Carson has few fields left to conquer, but his ambition still burns. 'I can always try to reconquer, and while I'm doing it, I've got to keep proving myself,' he explained. 'I don't get rides on my past record, only on what I did last time. It's a high-profile, competitive game, and if you don't keep your head in front, you fall by the wayside, no matter who you have been.
'I don't know why I keep going. I'm not a thinking sort of person. I don't analyse and agonise about my reasons. At the moment, it's my job, I still enjoy riding horses, and I just go and do it. I'm just an ordinary hard-working jock.' The little man does not do his thought processes justice; he is bright, and, when on form, one of the most outgoing, articulate and helpful of sportsmen.
He is also durable, brave, and almost obsessional. His path to the top - anything but smooth, but absolutely the last thing he would want is any sympathy - began in a blaze of mediocrity 35 years ago. He finished last on his first public ride, in May 1959, and it took him another three years to ride his first winner, Pinkers Pond at Catterick, and two more to lose his apprentice claim. He was one of the slowest-starting champion sportsmen in history, but his tenacity and desire to succeed clawed him through.
His childhood on a council estate in Stirling was not deprived, but not privileged either. His father Tommy was a foreman at Fyffes bananas, his mother May a part-time waitress. In those days he was Billy, a good Protestant name in a sectarian city, and there may lie a clue to his character. The Protestant work ethic is unforgiving; the fear of failure can haunt a life.
Carson's grandfather was a local rogue who had greyhounds and the odd tinker's trotter, one of which was the first horse wee Billy sat on. The classic racing film Rainbow Jacket made him see his tiny size as an asset; he paid for riding lessons at the age of 12 with a paper round, and at 16, having long lost interest at school, left home to seek his fortune in a racing stable at Middleham.
He would be one of the last jockeys around today to have gone through the stable-lad-in-rat-
infested-hovel routine. The likes of Eddery, Piggott, Dettori and Swinburn all came from comfortable horsey backgrounds - they had silver spoons by comparison, though they had to do their own digging. But Carson's breaks eventually came, and after his early years with the tough Armstrong brothers, Gerald and Sam, retainers with Lord Derby at Bernard van Cutsem's, Clive Brittain, Dick Hern and, most recently, Hamdan Al Maktoum, owner of Nashwan, Salsabil, Dayjur and Erhaab, gave him the opportunity to show off his considerable talent.
The highest of the high spots is still his Oaks win on the Queen's filly Dunfermline in Jubilee year, 1977. He won his first Classic on High Top in 1972, the same year as he won his first championship. He rode six winners from seven rides at Newcastle four years ago, he has ridden a century of winners 21 times, became the first jockey to breed and ride a classic winner, Minster Son in 1988, and was awarded an OBE in 1983.
There have been desperate times, too, in public and private life. He has been terribly injured twice, once in a car crash on the A1, and once in a race, when a filly broke both forelegs in a nightmare fall. As the Eighties progressed, he found himself overshadowed by Pat Eddery and Steve Cauthen. Intensely loyal to Dick Hern, he was deeply upset by the old trainer's sacking by the Queen five years ago. His first marriage broke up publicly and acrimoniously, and a second serious relationship also failed. His current wife, Elaine, has given him stability and some peace of mind.
The publication of his autobiography last year caused some flurries in the dovecotes and more tabloid headlines. Its frankness, particularly towards members of his family, cast doubts on the genuineness of the chirpy image. Carson said: 'Perhaps people that have read it do see me in a different light, but I have always been the sort of person that says things straight out. I may be many things, but I am not two-faced, and I think it is better to be honest, then at least people know where they stand.
'Some of the things I said were taken out of context, and weren't really as bad as were made out. I did say my sons were stupid, but only because they didn't listen to my advice. And two out of the three agree with that.'
Carson knows he will not win another championship - his last was in 1983 - because he will no longer chase countrywide for rides. But his appetite for the job he has been doing day in, day out, through five decades, remains strong, so long as the good horses are there, and he is still remarkably fit. 'Riding is one thing that does get easier as you get older,' he says. 'You've seen it all before, it's not so stressful, not such a big deal. Perhaps you haven't got the quickness that you once had, but you've got the experience, the stamina. And that can get you through.'
Nearly all the top jocks nowadays write (or have ghosted) columns in newspapers. Carson is no exception, and the suggestion that perhaps journalists should start hanging hopefully round the weighing room was met with a gale of Question Of Sport cackles. His contract with another organ means that he cannot talk in detail about Erhaab's chances on Wednesday, and your correspondent's frustration at not being able to discuss this produced more giggling.
He does, however, take the Derby seriously. 'It's still the race to win, the one that everyone wants. It would be wonderful to do it one last time, but it will not be easy. Everyone keeps saying it's an open race; that's rubbish for a start, there are only five or six in it with a chance, the rest are just making up the numbers to give their trainers a runner.
'They say there may be traffic problems with a big field, but that's rubbish too. If you're on a good horse you don't get into trouble, because a good horse can take you out of it. And I don't hold with the excuse that a horse didn't act down the hill. If it doesn't, then it's not good enough. That's why they run it at Epsom, to test all aspects of a horse's ability.'
Carson is one of the most sympathetic of horsemen, and the punters love his active, busy style - visibly on their side - and if he pumps Erhaab home, pleasure on both sides will be genuine. His great friend and colleague Pat Eddery said: 'If they keep oiling him, he'll go on for ever.' He won't, but victory on Wednesday would crown the golden autumn of the career of a man who has proved the Captain Scarlet of his trade: indestructible.