A black Mercedes pulls up to the curb in a central London street, and out steps Sachin Tendulkar. There are no crowds, no bodyguards, and no one pays any attention to this stocky and unremarkable gentleman who, aside from a chunky watch, looks like any other office worker as he stops to make a call on the pavement.

Tendulkar wanders up and down the busy street, tourists and Londoners walking past him, enjoying the midsummer warmth and the rare anonymity. It is a mundane act for the rest of us, but a treat and something to revel in for him.

"I like it here, I have more freedom to do whatever I want and move around without any problems," he says. "I enjoy that feeling, it is very different for me. I am given my space, which is important, and I can go for nice walks in the parks."

While his Indian team-mates were unsuccessfully attempting to defend their World Twenty20 title, Tendulkar was here to spend time with his family at their London home. He watched cricket from the stands, went to the men's final at Wimbledon, took a trip to Iceland to sample some cold weather, took his nine-year-old son Arjun for net sessions at Lord's, and simply enjoyed unmolested trips to the cinema and restaurants.

When asked if he could repeat any of these pursuits in Mumbai he laughs and looks utterly astonished at the question. "No, no, no, I couldn't do any of that, I have not done it for a long time, and I don't see myself doing it again, really."

Back home in India, of course, Tendulkar is an icon. His every movement and utterance are monitored, while his image is on billboards and in as many as a quarter of all advertisements on Indian television. Tendulkar recalls one public appearance several years ago in Bangalore when nearly 200 policemen were needed to control an impromptu crowd of up to 7000 people after word had spread he was in the city.

"There have been a few scary moments, but that was the worst. It was out of control, and there didn't seem to be enough policemen," he says. "A lot of people wanted to get close to me. It was just affection, but there was a chance of me or others getting injured."

To avoid a repeat, Tendulkar rarely ventures out, or when he does it is in disguise or very early in the morning. "I have sometimes worn a baseball cap, a beard, spectacles and a wig not to be noticed," he says with a smile. "It was just a bit of fun, and I was once getting away with it until I dropped the spectacles and a couple of guys recognised me.

"I also love going for a drive at about 5am, when the roads are empty and people won't see me. I am not driving fast, just 25mph. I listen to relaxing music, there is no one else. I like it being just me on my own."

Today Tendulkar has come to the Opus store in Covent Garden to promote his own forthcoming Opus, a mammoth 800-page book weighing 30 kilos, which will tell the story of his career. Tendulkar is only the second sportsman after Diego Maradona to be given such lavish treatment.

Tendulkar remains humble and warm, obliging and polite, speaking in a soft voice. In a room decorated with large images of Tendulkar and his greatest innings, he will later hold a press conference that offers a glimpse into the madness of his life. It begins with a nurse taking a swab of saliva for his DNA profile, which will then become a work of art for his Opus. It ends with a gaggle of fawning Indian journalists, prefacing their questions with statements such as "I would like you to know I named my son 'Sachin' … "

"I always play in pain, all the time. The last three months I played with a broken finger, but you know when pain is manageable or not and most of the time I can do it"

Tendulkar is at pains to make clear that the launch of his Opus does not signal the end of his career, and while at 36 it is inevitably approaching, he has set no retirement date, even privately.

"I have given it no thought at all," he says, "I am good at cricket, so I will play a while longer. I still love the game as much as ever. It is my job, but it remains my passion too. This is fun. Cricket remains in my heart."

As the scorer of both the most Test and one-day runs, as well as the most Test and one-day centuries Tendulkar's standing as one of the modern game's greatest players is secure, and the 2002 Wisden argued that only Sir Donald Bradman can claim to be better in the entire history of the sport. Even so, he is far from sated. He wants more. Tendulkar once said being satisfied is like pulling up the handbrake on a car and expecting it to keep moving forward.

"I am not pleased yet with what I have done," he says shaking his head. "Sunil Gavaskar has told me that I have to get to 15,000 runs. He said he would be angry with me, he would come and catch me if I didn't. I admire him so much and to score that many would be a terrific achievement, but that is not the only aim." What else? "Winning the World Cup in 2011."

To prolong his Test and one-day career Tendulkar has decided not to play Twenty20 internationals. "I felt as though I would have been a loose link in the team, I couldn't do that to them," he says. "I was not sure I would last, there was something missing. If my body wasn't strong enough to last through the tournament then I couldn't play."

At 36, does he feel his body is letting him down? He pauses to think. "No, it still does what I want it to, but I am older, so it is different. You just have to work harder. There are moments when I try something and it doesn't happen, but it isn't because of my age.

"I always play in pain, all the time. The last three months I played with a broken finger, but you know when pain is manageable or not and most of the time I can do it.

"I can still do what I did when I was 25, but the body is changing, so your thought process has to change too. I have had to change how I think, which is about taking less risk."

In recent years Tendulkar has tightened his style, becoming increasingly cautious, but he remains as prolific as ever with an average of 52.11 over the last 18 months. The last year also contained what he considers to be his greatest innings, the unbeaten 103 he made against England in Chennai, for the performance but also for its defiant symbolism: it came weeks after the terrorist attacks in Mumbai.

Even so, some figures in the game have suggested Tendulkar's powers might be on the wane, including the former Australian coach John Buchanan, who has said he might be losing his confidence against short and quick bowling. Tendulkar's eyes narrow and he looks close to being annoyed before laughing loudly.

"It is only his opinion. John Buchanan doesn't have to be right all the time," he says with a knowing smile. "If I couldn't handle short deliveries, then I wouldn't still be scoring runs. Maybe he needs to change his opinion… There must be something very wrong with all the bowlers around the world that they have allowed me to score so many runs."

After two decades playing international cricket, how has he so ruthlessly accumulated these runs? "The secret to batting is to stay still and just react to what the bowler has done," he says, making it all sound simple. "You have to be still both in your mind and physically. It is so important that your mind is not full of a lot of thoughts because your reaction time is not going to be good. You have to keep your mind blank.

"The toughest thing is to clear your mind. The mind always wants to be in the past or the future; it rarely wants to be in the present. My best batting comes when my mind is in the present, but it doesn't happen naturally. You have to take yourself there. I am not able to get in that zone as often as I would like, but when you are there you don't see anything except the bowler and the ball. You have to allow your instincts to take over. Trust me, your instincts are 99% right, but you know, the older I get the more I realise how important your breathing is to good batting. By that I mean, if you focus on breathing and relaxing, you can force yourself into a comfortable place to bat."

And when the end does finally come Tendulkar says he will not resist it: "I will know when it is the right time, I won't have to be dragged away… I am the person who will make the decision, and I will know whether I still belong." And what will he do afterwards? "I would like to do something with the game."

How will he adjust to life without playing cricket? "It is a scary thought," he says candidly. "It has been there for my whole adult life. It will be difficult. I have been around for a long time. I can imagine when I finish I will long to face just 10 more balls but you have to move away."

Who will surpass Tendulkar's record haul of runs? Bradman anointed Tendulkar the player who most reminded him of himself and picked him as the only modern player in his all-time XI. Would Tendulkar extend the same compliment to anyone? "I would say Virender Sehwag comes closest to my style."

What state will Tendulkar leave the game in when he does eventually retire? He made his name in Test cricket, but he has significantly added to his fortune with the emergence of Twenty20 as captain of the Mumbai Indians in the Indian Premier League.

"There is no way Test cricket is dying," he says. "Twenty20 cricket is the dessert and you can't survive on that. Who wants to eat only desserts? Test cricket is my main course, with all the meat and vegetables, and then it is nice to have Twenty20 as a dessert."

But does he have any fears about the growing influence of Twenty20 cricket? "I started playing cricket at six with a tennis ball not because I wanted to be a millionaire but because I loved cricket," he replies. "Maybe in 10 years or even now, people will pick up cricket bats thinking only about the huge money in Twenty20 cricket. Money should just be coincidental. The passion and the desire are the most important thing. I worry about runs, not contracts."

"It [retiring] is a scary thought. Cricket has been there for my whole adult life. It will be difficult. I have been around for a long time. I can imagine when I finish I will long to face just 10 more balls but you have to move away"

Following the attacks on the Sri Lanka team in Lahore and those attacks in Mumbai, which prompted the IPL to relocate temporarily to South Africa, Tendulkar has seen terrorism pose an increasing threat to cricket.

"It was a horrible surprise… I was shocked about what happened to the Sri Lankans. I always thought that sportsmen would be left alone and we wouldn't be targeted."

Would he ever feel safe touring Pakistan again? "It is not up to me to judge whether it is safe; it is up to the government to make those decisions once they have done their homework." And that would be enough? "Probably, yes."

A couple of hours after his arrival, a small band of mostly Indian students are now milling around the front of the store and attempting to take pictures of Tendulkar through the windows.

They are open-mouthed when Tendulkar then steps outside to meet them and sign autographs before strolling down the street, with two unnecessary doormen, to pose for a photograph in the middle of Covent Garden. Once more, even accompanied by a photographer this time, no one gives him so much as a second look. And that is just the way he likes it.