It's a freezing cold afternoon, nuclear-winter grey, the feeble light fading fast. This little pocket of north London, squidged between Green Lanes and the A10 with the North Circular looming ahead, never looks much like the Riviera, but today it's particularly dank and depressing. In the concrete approach to the White Hart Lane Community Centre, a coach is firing questions at his charges: "Was you happy with that, goalie? Was you? You know the rules of football." It's not clear which of the three teenage boys carefully studying the ground before them is the hapless goalkeeper, but they all look suitably chastened.

Inside, things are a lot more cheerful. Staff bustle about, setting up training sessions for boxing, table tennis, football. Kids begin to come in, a trickle at first and then a flood – mainly boys, but a bit later a girls' wrestling team can be spotted doing sprints across the gym. There's a hum of enjoyment and effort. This is the Skills centre, a project run by the Tottenham Hotspur Foundation to provide young people between the ages of 12 and 19 with a space of their own – crucially, as they tell me, a safe space. And its public face – the face that is emblazoned on its logo and signage but, more importantly, lodged in the hearts of countless local football fans – is that of Ledley King, the Spurs defender and captain who, after his retirement last year, is now a club ambassador. King joined Tottenham as a 14-year-old trainee, and spent his entire career there; as the cliché goes, he lives and breathes the club. So what does a professional footballer do when it comes time to hang up his boots?

I've spotted Ledley before he arrives this afternoon; he's in a photograph on the wall, captured smiling in a pair of overalls, paintbrush in hand, mucking in as the centre gets a makeover. And, of course, I know him straight away when he comes through the door – after all, he's famous and I'm waiting for him. But it's definitely not because he makes a fuss about it; and not even because the visitors to Skills do either. Sure, they gravitate towards him, especially when we head outside to the football pitches; they're clearly excited that he's here and they're delighted if they get a moment of his attention. But there's nothing remotely approaching your usual celebrity-inspired furore; it's a bit more like spotting your favourite cool cousin at a family wedding.

A little later, I sit in as Ledley chats to Daniel, a quiet, polite teenager who captains the Skills side and has just done his Level 1 coaching badge. They talk about what Daniel's got out of the organisation – not least the fact that, coming from nearby Northumberland Park, he has to travel to Wood Green; nothing in terms of distance, a lot in terms of the postcode pecking order that fuels much of the area's gang rivalry.

"It's just trying to educate people that we're all the same," explains King. "We're all part of one community and we're all trying to work together to better ourselves." When Daniel asks him what it was like to captain his team, he turns it round to emphasise what connects the pair: "Yeah, well, you're captain, too, aren't you? How do you feel about it?"

Through all the time I spend with him, here and at Tottenham's brand-new, space-age training ground, with groups of kids and other Spurs staff and one-to-one, he remains the same: shyly diffident, always friendly but occasionally almost solemn, and perpetually keen to play down his own achievements. But there are flashes of something else beneath. "Did you always know you were going to make it?" asks Daniel. There's a long pause, and then: "I did. I shouldn't say I knew. But in my head I was confident I was going to make it."

Mention Ledley King's name to any Spurs fan, and all the most treasured footballing epithets spill out: legend; icon; hero; one-off. The words are hackneyed, but the sentiments are not. King spent his entire playing career at the club, becoming its first-team captain when he was 23. He grew up in Bow, joining the celebrated Senrab youth team when he was just seven or eight, playing alongside future England internationals John Terry, Bobby Zamora and Paul Konchesky. Do they still talk about it if they meet up now, I ask? "Bobby Zamora even mentions it on the pitch to me when I've played against him," he laughs. At the time, though he is coy about admitting it, he was a Millwall fan – just following his best friend's dad, who took him to matches. As soon as he was old enough to pick his own team, he assures me, it was Spurs all the way.

Leading by example: King inspiring youngsters at Tottenham's training centre. Photograph: Shamil Tanna for the Observer

In 264 league appearances, he was the bedrock of Tottenham's re-emergence at the top of the game, leading them to their last major honour, the 2008 Carling Cup, when they beat Chelsea in extra time. He had the speed and power of traditional British defenders allied to the two-footed technical skills of a continental sweeper; indeed he could easily move out of central defence and into the midfield. He won 21 international caps, and in a generation that included Terry and Rio Ferdinand, he was the outstanding English defender. He was, said Arsenal's Thierry Henry, who was at that point the world's greatest striker, the only player in the Premier League who could relieve him of the ball without committing a foul.

At Tottenham, his status was further enhanced by the fact that he stepped into the boots left vacant by Sol Campbell's contentious departure in 2001 for local rivals Arsenal; to add insult to injury, Campbell's contract had expired and the club received no money for him. Spurs fans have never forgiven Campbell for the manner in which he left; his perceived disloyalty has only underlined King's determination to succeed at the time and his subsequent steadfastness. "It was as though your heart was broken, and you think you'll never love anyone again," one lifelong supporter told me. "And then the next day, the most beautiful woman in the world walks into the room."

The happy ending suggested by that rather florid description, though, has not been without its shadows. Since his mid-20s – he is 32 now – King has struggled with serious knee injuries; rarely is his career spoken of without a little nod to what might have been had he stayed fit (100 England caps, for example). For the last five years of his playing days, he wasn't able to train with the rest of the team, spending his days on the treatment couch and undergoing carefully supervised training regimes in the gym. It was a strange and solitary life – and a lot of the time, football seemed very far away. "There was a little ball in the physio room," King tells me, "and sometimes players would just take it out and start kicking it around the treatment room, even though we wasn't allowed. Because we're footballers. For me, it was the only time during the week when I got to see a ball."

There is a strain of melancholy to King, underneath his very pleasant and open manner, and I wonder how much these years took out of him. "There was a lot of times when I felt like I was in a dark place, on my own, trying to get through the injuries."

King's natural talent and dedication was such that managers did everything they could to extend his career, and he himself became focused simply on keeping going: "I didn't think about retiring. Because I was always finding a way, up until the last half of the season, to get through." He had no idea when the moment would come, he says, but eventually it did. "It was only the second half of the season that I felt I couldn't do what I wanted to do, my body wasn't reacting, and even then I was still thinking, maybe at the end of the season, I'll look for an alternative treatment, or some way around it… so I was never really not thinking about playing, I was always thinking about finding a way. But I suppose there comes a time when you can't put your body through it."

He finally retired in July of last year, and was then faced with the inevitable question of what to do next. In some ways the unconventional life he had been leading made it easier; he didn't have to adjust to a sudden loss of daily camaraderie. He was also able, for the first time, to loosen his mind a little: "Because physically I couldn't do it, there was a lot of mental strain, trying to prepare myself to put myself through the grind and keep up with everyone else and try to stay on a level playing field. There was a lot of mental stress. So I've switched off in that respect."

But his single-mindedness has also made it harder. While he concentrated on prolonging his playing days, he wouldn't allow himself to think of anything else; not even something blandly relaxing. "A lot of the lads like playing golf, and I was kind of intrigued" – he says this as though he were talking about snowboarding in the Andes – "but I didn't want to play it because I didn't want it to take up my time or my concentration while I was still trying to play football." He does let slip – it even seems to surprise him – that he once owned a horse, with Ashley Cole. "It wasn't really for us… We lost interest pretty quick." What was it called? "King of Defence." What else?

Not a golf-playing racehorse-owner, then. Neither, it seems to me from talking to him, would King much enjoy a life in front of the camera; he's both intense and articulate in conversation, but never comes across as someone who loves to talk, who must get their oar in at all costs. Unlike many football pros, he has no time for Twitter. An increasing number of players plump quickly for a life of television punditry and some – a recent notable is Gary Neville – are excellent at it; but you can't see it being King's idea of fun.

Back in the day, footballers retired to run country pubs. Nowadays, they don't actually need to do anything; if you've had, say, two Premier League contracts, you're set up for life. But sitting around your mansion – they used to be mock Tudor, now they're the real thing – isn't enough for everyone. Some go thespian: Vinnie Jones was last glimpsed in an episode of the Sherlock Holmes retread, Elementary, playing an assassin who turned particularly nasty if anyone interrupted him when Arsenal were on the box; Eric Cantona, Frank Leboeuf and David Ginola have done similar. Others shuffle their property portfolio, take to the airwaves – TalkSport's roster of former footballers includes Alan Brazil, Andy Gray and Jason Cundy – or join the after-dinner speaking circuit.

Those with long-term affinities to one club can also find themselves sticking around. For the moment, King has a dual plan of attack; his ambassadorial role at Spurs and the painstaking steps through the various stages of coaching qualification.

Under attack; Thierry Henry of Arsenal tries to get past King at White Hart Lane, December 2002. Photograph: Tom Jenkins for the Guardian

He is clearly well-suited to the former. Even without partisanship – there are plenty of Arsenal fans at Skills – youngsters clearly respond to him. "I'm just like these kids," he says. "That's what I try to let them know, that I was just like them when I was younger." The MP for Tottenham, David Lammy, backs that up. "Most of the young people in my constituency are like Ledley King," he told me, explaining that King had recently accompanied him to a local college. "He's very unassuming, he's very down-to-earth. He didn't come with great fanfare. He is the quintessential regular guy." He feels that King's story of application and dedication is one that can inspire many of the young people who live in a borough that is in the middle of a long regeneration process.

Another career path is, of course, management – and that's why King is also spending plenty of time in the leafier environs of Enfield, where Tottenham's new training ground sits. It is a world away from the Skills centre; when I drive up Hotspur Way (yes, really) and into the car park, the only space I can find is between two very shiny sports cars. Since I suspect their stereos cost more than my car, it is a nervous moment. Inside, I stand in a vast, shiny indoor arena watching Ledley having a laugh with Michael Dawson, his successor as club captain, before he sets to work putting a schools group through their paces.

Does it come easily, I ask him afterwards? "It's quite alien to me," he replies. "I've been a footballer my whole life… It's a learning process for me, to command a young group and instruct them to do what I want them to do." He emphasises that, for the moment, he's simply keeping his options open, although he concedes that management, for all its uncertainty and pressure, is an alluring thought: "I've kind of got that feeling that I would really like to see how I'd be as a manager, what I know tactically – that's a long-term goal, to see what I do know about the game."

Football management is, of course, notoriously precarious; and to date it has also seemed hard for black managers to gain a foothold. I ask him whether that's something that's on his mind: "It's a difficult one for me to talk about until I'm in there. Then I'll see. But it was something that was mentioned, and it's disappointing to hear."

At several points during our chats, King says that he thinks he's adjusting well to life after football, as though he has learned from his years of injury that acceptance and stoicism are the best way forward. When I ask him if, despite his career highs, the money and fame he's earned, he ever feels cheated, he replies: "I did for a little while, then it just became about trying to do as well as I could with what I had." But when I also ask whether he felt a bit of relief when he finally retired, he says: "There was a little, but quickly you realise how much you miss the game, how much you love the game… especially the first time you don't report back to pre-season."

Almost as a reflex, not really as a serious inquiry, I mention that it goes without saying that any return to actually playing football is out of the question. There's a pause; the atmosphere changes. Afterwards, listening to the tape, I wince; I feel as though I've been unwittingly cruel, at the very least tactless.

"I think, yeah. I obviously am 99% sure, but you know, like I said… [he laughs] I'm pretty sure I'm finished. I hope I don't try and come back, anyway, but…"

Right. Cards on the table. If there was a magic wand or a revolutionary new treatment, would he want to come back?

"OK, yeah, of course I would. Definitely. 100%. If that happens, yeah… Some people get tired of football. I still feel fresh as a footballer. But my knee made me older than I was."

We are sitting beneath a huge photograph of him, arms outstretched to balance himself, leg extended to reach the ball. It is a picture of athleticism, control, will power. It's beautiful. What does he feel when he looks at it?

"Sometimes I'll see pictures, I'll see clips and I think, 'Wow, I've finished, there's no more of that.'"