Wedged behind the sink taps in Dr Judith Yates's consulting room is a wall clock with a random sequence of numbers displayed on it. Where one might expect to see the figures 3, 6, 9, 12, instead the dial reads 9, 1, 5, 7. "One of my patients gave me that," she says, beaming proudly. "He made it especially, because he said, 'You don't have any sense of time, Dr Yates!'"

The clock's hands imply the time might be 10 past two – or is it 20 past nine? Or quarter to six? It's impossible to tell. I start to panic mildly about catching a train home until she tells me my first guess is correct. Then she checks the clock's time against her computer and looks up sheepishly. "Actually, it's not right at the moment, it's got its own mind …"

Notwithstanding the odd timekeeping hiccup, Yates's patients clearly hold her in high regard. Her desk and shelves are festooned with postcards and holiday gifts, including a porcelain Delft house replica from Holland, and salt and pepper pots from Trinidad. "Sometimes they even bring me cabbages and potatoes," she says cheerily.

But time is running out for Yates to add to her collection; next month she will retire from her position at the Wand Medical Centre in Highgate, Birmingham, where she has spent her whole career as a general practitioner and, latterly, a partner. Over the course of almost 30 years she has worked at the heart of one community, where patients have become friends spanning several family generations.

"Now I'm coming to retirement I am having people saying goodbye to me, which is most strange, because these are people I've known for years," she admits, a little forlornly. "I saw a lad last week who I first met when he was two, and he's now 31, so I've known him for the whole of his life. And other people my age had children when I had my children, and their children have grown up as mine have. It has been fascinating."

It's not hard to see why her patients keep returning. Yates has that reassuring aura common to so many GPs, somehow giving the impression she might be able to eliminate all traces of illness simply by force of will. I have to fight the urge to roll down my sock and ask her to look at my sore ankle.

Yet such longstanding relationships with her patients mark her out as a dying breed in primary healthcare. "Young GPs coming in now may not have that privilege," she admits, pointing out that modern surgery systems no longer allow patients to book follow-up appointments with the same GP three or six months in advance, only with whoever might be available.

How, I wonder, does Yates manage to circumvent this for the benefit of her own patients? "I forward book my own appointments," she says, laughing. "It's my privilege as a senior retiring GP. No one else in the building can do it."

While it might seem a long time to spend in one place, her many years in the inner city have given her a wide perspective on people and the world at large. "It's an area where people arrive," she says, telling me about the waves of immigration Highgate has experienced, from the Vietnamese boat people in the 1980s to survivors of the Montserrat volcano in 1995.

And, of course, over time many of those survivors have passed through the doors of the Wand and occupied the seat beside Yates's desk where I now sit. "People still talk about the volcano now, they can't ever go back to their homes," she says. "Then people came from Hong Kong, when it went back to China. And obviously there are people escaping from the wars in Iraq and Somalia. They all land here and tell us their stories of the world."

At the heart of this observation is a key skill for every successful GP: the ability to understand their patients and identify their needs. "It's like a detective story," she exclaims, rising enthusiastically to the theme. "It starts with my medical knowledge, but it's about listening to them, listening to what they're explaining."

Often this is easier said than done, because people will use completely different words to describe the same things. "But it helps if you know the person, that's the benefit of continuity of care," she points out, in a gentle swipe at the current trend for GPs to move around every few years.

Inevitably though, many of the health issues Yates has dealt with in Highgate have been perpetuated by hardship. Over the years, substance abuse has become her specialist area of concern, and in retirement she intends to continue working two days a week at a new alcohol and heroin detox centre in central Birmingham.

"That part of my work has grown and it has been a treat alongside my primary healthcare work," she says. "Sometimes I've got to see people who have been very damaged in their childhood, who have had a lot of grief in their lives. But there's another group who tend to be more experimental, more risk-taking with their lives."

To keep in step with this group, much of Yates's work has lately involved monitoring the rise of designer internet drugs such as mephedrone (which was recently criminalised). A simple method of doing this is by using Google Trends, a function of the search engine that reveals what people look for most online. "If you look there, you can see searches for ecstasy use have gone down and mephedrone has shot up," she says, tapping away at her computer keyboard.

Given the internet's role in the spread of so-called "legal highs", it's a little surprising to hear that, on balance, she thinks the web has had a positive impact on substance use, giving users more information to base their choices on.

Changing attitudes

Figures for heroin and cannabis are also going down, she points out, but cocaine use is still rising, "which is a problem, as it's much more dangerous physically than heroin".

Yet at the time Yates was starting out as a GP in the 1980s, hard drug use was still relatively uncommon in Birmingham. "There were very few people using heroin," she recalls. "Then a great flood of brown heroin came in. Because it came from Afghanistan, people bought it instead of cannabis, apparently, and smoked it – before that, all people had known was white heroin. Then they used to wake up stark rattling and realise they had a dependency."

Such changing attitudes to recreational drug use are central to a campaign she has become closely involved with to test for and treat hepatitis C among former intravenous drug users.

Untreated, hepatitis C can lead to liver cirrhosis or cancer, although carriers can be cured if treated in time. But as the disease can sit dormant for years, many people, particularly who are aged in their 50s and 60s, may not be aware they have it. "The 1970s and 1980s were when most of our patients in Birmingham caught hep C," Yates explains. "It was before HIV, so people didn't have the same fear of sharing needles."

She urges anyone who injected drugs or even shared a cocaine straw during that time to get themselves tested, "even if you only shared a needle once, because that's what people used to do". People born in South Asian countries, she explains, are also at high risk as they may have received medical immunisations via shared needles in the past.

The phone rings; it's someone wanting a repeat prescription and Yates briskly reminds the receptionist that she is off duty at the moment. Clearly, being firm about switching in and out of work mode is a prerequisite for surviving the demand-heavy life of a GP, but I wonder how easy this really is?

She looks hesitant. "There is a bit of me that is always a GP, actually," she admits, a little reluctantly. "If somebody's ill wherever I am, I do tend to go into GP mode."

And what, I have always wondered, do GPs tend to do about their own medical needs? Do they pop down to their own GP, or into the surgery next door, or simply diagnose themselves?

"Like many GPs I suppose I don't go to the doctor as often as I should," she says looking surprisingly shamefaced. "I do have some GPs as patients and they're usually very polite and careful. You just have to say, 'What is it that you think is the matter with you?'"

She giggles at the absurdity of it. "That is not always straightforward. It can be difficult."

For now though, we have already chatted for longer than we planned. No doubt the partners already have something in mind, but they could probably do worse than give Dr Yates a proper clock for a retirement gift.

More information about hepatitis C is available on the NHS website

CV

Pay Salaried GPs employed directly by primary care trusts earn between £53,249 and £80,354, dependent on, among other factors, their length of service and experience.

Hours In theory, Yates works five-eighths of a full week, but in reality it's 2pm-8pm on Mondays, 8am-6pm on Tuesdays, 8.30am-9pm on Wednesdays, 9am-7pm on Thursdays … 'This doesn't sound much like a part-time job, does it?'

Work-life balance 'We're self employed so we have a lot of autonomy over moving our hours. I have had four children and I've been able to work longer or shorter hours, which I wouldn't have been able to do if I had been an employee.'

Highs 'The people I've shared my life with in this area, seeing people do well and seeing people who've had struggles get beyond that.'

Lows 'The emotional impact can leave you flattened. Also, the uncertainty of not being sure what is wrong with someone. You have to learn to accept you don't know everything.'

Overtime

Overtime For lunch, Judith always has sandwiches in the staff room with the other GPs. 'A nice bit of mature cheddar on wholemeal is fine.' Judith finds TV medical dramas a bit too close to the bone, 'But I was once shortlisted with one of my GP partners to be medical advisers to The Archers. We lost out to a casualty officer.' To relax, Judith is learning to keep bees. 'We spend a lot of time at our house in a community in Shopshire where there are five beehives. We also share 12 chickens and we are about to get three pigs.'