I am waiting to speak to Ben Ainslie at the Royal Ocean Racing Club, a grand Georgian townhouse next to St James's Park in London. To be honest, I'm surprised I've been allowed in – I'm not dressed for a yacht club. It's a relief to see that Britain's most successful sailor is also in jeans. He's being interviewed by television news first. It's not often that TV news bothers much with sailing, but Ainslie's in demand. He's just won the America's Cup, the biggest prize in the sport.

I'm surrounded by books on yachting and pictures of yachts and past commodores. Yachty history everywhere. Time for a bit more …

August 1851, Cowes

An American schooner, called America, wins a race round the Isle of Wight under Queen Victoria's nose. The boat's owners return across the Atlantic with their prize and lay down the rules for the America's Cup, a challenge trophy to promote friendly competition among nations. Since then the competition hasn't always been friendly, but the Cup has become the most coveted in world sailing. A lot of very rich men have spent an enormous amount of filthy lucre trying to get their grubby hands on it.

August 2005, Cowes

A team of young trainee keelboat sailors is captained for one race in the Solent by Ben Ainslie, then 28. He's already a star. The previous year he won a gold medal at the Athens Olympics. Four years before that, in Sydney, he also won gold. And four years before that, in Atlanta, he won silver, when he was only 19. He will go on to win golds at the 2008 and 2012 Games, too, making him the most successful Olympic sailor ever.

This race in the Solent has nothing to do with the Olympics, or the America's Cup; it's of little significance in Ainslie's glittering career. So why mention it? Well, as well as him, and the trainees, there's someone else on that boat (a Farr 45 if you're interested) that day: me. It doesn't matter why – journalists can sometimes blag a ride, I like sailing, blah blah. It just means I have seen him at work, doing what he does.

The race doesn't go well, initially. The young navigator cocks up: we go the wrong way, and rip a sail. We're playing catch-up. But Ainslie, driving, claws us back into it with a focus, a single-minded mechanical determination and a competitiveness I've never seen in anyone else. I'm scared of him, and I'm on his side. He takes big risks, passing within what seems like inches of ships. Approaching the finish line, we're on collision course with another yacht. Ainslie yells at it to get out of the way, claiming he has right of way (he doesn't, he later admits). The other skipper makes way, terrified, and we cross the line, winners. Of course. This is a man who certainly knows how to win. Jesus, imagine how he is in a race that actually means something to him.

Ben Ainslie lifts the America's Cup trophy after Oracle Team USA's victory in San Francisco last month. Photograph: Josh Edelson/AFP/Getty Images

There are better, and better-documented, examples of Ainslie's ferocious competitiveness, which at times can appear to border on psychopathic. The way he hunted down a Brazilian sailor, unsportingly some said, to ensure gold in Sydney; a human-torpedo assault on a press boat he took offence to; the rage at the Olympics last year ("They've made me angry and you don't want to make me angry"), which of course spurred on the charge to yet another gold.

What strikes me most, though, seeing it in the flesh eight years ago, is how he is unrecognisable from the man I met the previous evening, who was quiet, shy, unforthcoming, unconfident even, and barely noticeable. Put him on a boat though, and he turns into an animal.

September, 2013, San Francisco Bay

(This part you probably know by now.) The final of the 34th America's Cup, the competition that started 162 years ago in Cowes and is now the oldest trophy in world sport, looks like it's all over. The holders, software billionaire Larry Ellison's Team Oracle USA, are being outperformed and outsmarted by the challenger, Emirates Team NZ. In a desperate, last-ditch attempt to salvage the situation, Ellison does something bold. He sacks his tactician and puts a new one on the boat: Ainslie (who was already with the team, skippering the practice boat). The results don't change immediately; they lose another couple of races, until the Kiwis are 8-1 up in a first-to-nine competition. They're a whisper away from winning it, when a race they're easily winning and nearly finishing is abandoned because the time limit is passed.

Then the tide changes, and something clicks on the US boat on which Ainslie is calling the shots. They start winning. 8-2, 8-3, 8-4 … 8-8. Then, last Wednesday, in a thrilling final race, the Kiwis make the better start, but the Americans reel them in, pass them on the beat upwind and win by 44 seconds. It is undoubtedly one of the most extraordinary comebacks in sporting history. At the heart of it is Ben Ainslie.

October 2013, Royal Ocean Racing Club

We've caught up with ourselves too, the TV news is done, and now we've got the Fastnet Room to ourselves. Well, apart from his manager, and a lawyer. Anyway, nice one, the America's Cup! How did he do that then? "Well, it's not a case of how did I do it … " Oh, here we go – he's going to be all modest, and it's going to be all about the team effort, zzz. "No, it's true. It is a team effort. There were 120 guys on the team and 11 of us on the water. It's certainly not about individuals. I'm not just trying to be modest."

Come on, that's not what we're saying here – we're saying it was our sailing son wot won it. "Yeah, which is embarrassing." And he says that being compared to Nelson is embarrassing too (because Nelson did it for us maybe, rather than hiring himself out like some kind of mercenary, to the Americans). But you could hear Ainslie on the television coverage, shouting instructions. He admits that changes were made, of which he was one, and that they helped to turn things around, and that as a tactician he did have to make the final call.

What about when he was brought in halfway through, they must have hated him right? "No, they were fantastic," he says. Everyone was happy with the decision; well, maybe not the guy who got kicked off, but he was fantastic, too …

I think the problem is that I've got land Ben Ainslie here – polite, charming and saying all the right things. But it's not the same shy, invisible land Ben Ainslie I met eight years ago (he claims to remember that meeting, by the way; I don't believe him). I guess another couple of Olympics, a knighthood and now the America's Cup isn't going to knock anyone's confidence too much. He's certainly more relaxed than before, better company, chattier.

I ask him about the Jekyll and Hyde thing, turning into a different person on a boat. "I think I used to. I was very quiet on land, and did turn into a bit of a monster on the water. But now I think the two characters have sort of morphed. I'm more comfortable on land. There's no way, 10 years ago, I could have joined that [Oracle] team like I did, jumped on to the boat halfway through an event ... and started telling them what to do. That's just maturing."

That's not to say the monster is dead, though. We saw the odd glimpse of it, shaking both fists at the Kiwis after an incident at one of the starts, and in his angry moment at the last Olympics (after he felt he was penalised unfairly for something). Does he need that anger? "I seem to produce the best performances under pressure, when things aren't going that well. I love the challenge, being on the back foot. I think a lot of professional sportsmen love that adrenaline rush you get from being on the edge. It could all go drastically wrong and you've got to absolutely nail it to come through. It's incredible the sort of kick you can get out of those situations."

He's spoken before about being bullied at school. "I think it probably toughened me up a bit, made me want to prove myself, because when you're at school and you're not really great at anything and struggling a bit, then, you know … "

Is there's anyone in particular from back then he'd like to stick it to? You know, look at you, Colin Tucker (or whoever), stacking shelves at Asda – I just won the America's Cup, and I'm a Sir. But he's not having any of it. "It wasn't anything outrageous, it just wasn't particularly great." A lot of the bullying was to do with a sun allergy he has. "Obviously it wasn't the best sport to take up".

So now he's won medals at five Olympics, been knighted and won the America's Cup, all by the age of 36, presumably he'll hang his sea boots up soon and tell stories by the fire. A family, is that something he might do? Could he see himself teaching his kids how to sail? "Yeah, that would be amazing. I better sort that out at some stage soon. I'm getting a bit old, turning into a bit of a wrinkly old seadog."

There is someone; it's not easy, as she's living in New York at the moment. "So that has been quite handy, between San Francisco and New York." Interesting that he thinks a separation of 2,500 miles is "quite handy" in a relationship. I don't think he's being sarcastic. I'm wondering if Ben might not be the easiest boyfriend.

Anyway, not yet. Now he's won the America's Cup with an American team, and wants to do it again with a British one. Which means finding at least £25m a year for the three or four years until the next one. Will he be asking Keith Mills, who was instrumental in putting on the London Olympics and Paralympics and has been very supportive of British sailing, or Richard Branson perhaps? He doesn't say for sure. He says it's hard to talk about because he's still under contract to Ellison, but the way he speaks, I reckon they'd be on his list. He also says it will be hard to compete with the likes of Ellison, "a billionaire with an open chequebook".

Now is the time to act, though, with sailors and designers available after the end of the last one, and the buzz still on the breeze. It worked this time, he says, probably for the first time, as a sporting event and a television spectacle. Close racing, extraordinary high-performance catamarans almost literally flying around at over 50mph, proper athletes working their arses off, a spectacular setting, TV footage (which TV companies are prepared to pay for) and graphics that meant it was actually possible to know what the hell was going on, not to mention that comeback – it all came together into something properly exciting.

A comparison with Formula One isn't unreasonable, he claims, "with the speed of these boats, the performance thing, and the physicality". Like F1, the America's Cup needs to bring costs down. "If that's done properly then hopefully you will retain that level of excitement, getting a few more boats, and have a great circuit on your hands.

Isn't sailing just a sport for toffs, though? I'm looking round, at the Georgian panelling and the yachty portraits. "That's about the history of sailing," says Ainslie, who says he isn't a toff ("Do I look like a toff?"). "We've got a really proud maritime history, and it's beautiful. You wouldn't want to change that. But it's not America's Cup racing. That's the future. I see them as very separate. In the past it's been a sort of billionaires' plaything. Any sport at the highest level is expensive. Winning the Tour de France isn't cheap, and that's a cycling race. It's a misconception that sailing's about gin and tonics on the aft deck. This event, and the Olympics for the past 15 to 20 years, have shown that a lot of grit and determination and hard work go into it. It's not a toff's sport, it's a proper sport."

He gets quite passionate defending his sport, particularly about accusations of over-toffiness, it seems. Not too passionate I hope – we know what happens when he gets angry, and I wouldn't want to be on the receiving end of that, even on land. Your right of way, Ben – Sir Ben – even if it isn't.