Ben Lopez has spent 17 years bargaining with kidnappers – and he's never lost a hostage. The secret, he says, is psychological skill and gut instinct

'You must be John. I'm Ben Lopez."

"Good to meet you, Ben."

We both know he isn't called Ben Lopez, but we maintain the pretence. Everyone has to have a name and his might as well be Ben Lopez. For the past 17 years, Lopez has worked as a kidnap and ransom negotiator, a job in which his own safety – as well as that of the hostages – depends on his anonymity. Not that you can miss him in the flesh as he is 6ft 5in tall and about as broad. Which turns out to be pretty much why he came to be offered the job.

Lopez trained as a psychologist in the US and worked in a psychiatric hospital. Whenever patients threatened to become violent, the staff looked to Lopez to sort them out because of his size. "I enjoyed the challenge," he says. "I found I could control the patients into doing what I wanted without escalating the situation."

Thereafter the story becomes a little hazy until, at some point in 1994, he was asked to go to Colombia – "Did I mention I'm fluent in Spanish?" – to help negotiate the release of a hostage. It is possible even the first bit of the story is a little hazy too, as I wouldn't put money on Lopez having told me the right country. The only thing I would put money on is him getting me out alive. After all, a great many other people have done and he's yet to lose a hostage. "Touch wood," he adds.

Until the mid-70s, there were no openings for a career in hostage negotiation and even now the job description is fluid. "There are no hard and fast rules," Lopez says. "Just a bunch of very flexible, standard, safe operating procedures. Every situation is unique. Knowing what is the right move to make is often just a matter of gut instinct."

There are four typical hostage scenarios. The political/religious, the financial, the siege (eg a botched heist) and the domestic (when someone is held by someone who is emotionally disturbed – usually a family member). Lopez tends to get called in either for the political/religious or the financial, as these tend to take place in failed or semi-failed states where law enforcement is either virtually non-existent or corrupt and there is a good chance of the kidnappers having their demands met.

"The financial is definitely the easiest situation to handle," Lopez says, "because the kidnap is a straight-forward cost-benefit equation, with everyone having a vested interest in the hostage being kept alive. There is no money to be made out of a corpse. My job is to control the situation, to keep everyone calm, negotiate a price and the handover. The political/religious is much trickier because the aims of the kidnappers are less overtly rational as they tend to be more interested in getting publicity for a cause than in either their own or the hostage's survival. So the outcomes are far less certain."

Lopez never now negotiates directly with the kidnappers himself – most of his work is in Afghanistan and Iraq and he doesn't speak the languages. He selects the person who will do the negotiation – frequently, but not always, a family member – and write their scripts. Being on the wrong end of a negotiation is inevitably reactive as you have to wait for the kidnappers to call: Lopez's aim is to exert the maximum control within those limited parameters.

"It's a matter of judgment knowing how much you can push a kidnapper at any given moment," he says. "There's often a fine psychological balance to be played. The kidnappers don't want the situation to play out indefinitely: the longer it goes on, the more it's costing them and the more chance there is of something going wrong. But you also have to understand local variations: in South America a kidnap can go on for months or even years; in Afghanistan the average kidnap is over in weeks."

And then there is the ransom itself. How much is enough? "I can't tell you," he says. "I can't give away that information. It might give future kidnappers some leverage. What I would say is that you should never settle too soon, even if the kidnappers are asking for a sum with which you are comfortable. You don't want the kidnappers thinking it's money for old rope and there's plenty more where that came from. I know of a number of cases where hostages have been seized again by the same kidnappers within a matter of months when the ransom was too readily agreed."

What about Lopez's fee? "I'm paid on a per diem basis, though I never work more than three weeks straight. Any longer and I get burnt out. If necessary, I hand over the situation to someone else and return later."

And how much is his daily rate? "I'd rather not say." He has good reason not to. In some countries he has to work illegally as it is an imprisonable offence to profit from kidnapping. Which technically he is. "It's ridiculous," he says. "But what can you do?"

You tell me, I say. He smiles. "I'd rather not."

We seem to have hit a bit of an impasse. Time for another tack. OK, so let's say I was taken hostage, I say. When and where is it most likely to happen and what's my best survival plan?

"Assuming you haven't arranged your own kidnap?" Lopez replies.

What?

"It happens. People sometimes try to defraud their insurance. We always check that out as a possibility. In Britain or the US, your chances of being kidnapped are very small, so let's say you're living in South America. The chances are you will be seized within 10 miles from your home, though you shouldn't read too much into that as most journeys are less than 10 miles from someone's home. But you are most likely to be taken on your way to work when your mind will be on other things and you will be operating on autopilot."

Are there any signs to watch out for?

"People have told me that, on reflection they had noticed some suspicious activity, such as a member of staff acting oddly immediately before the kidnap, but it's hard to make those connections. His behaviour could just as easily have been explained by problems in his personal life as being an insider on the kidnap plot. Similarly, it's hard to tell if that car that's following you to work is definitely the same car that was following you the day before, or indeed, if it is, whether it's just a coincidence. Hindsight is infallible."

And when I'm taken?

"Just go along with it. Don't try to escape. You'll probably be taken in the street at a traffic light and you can't rely on passersby to notice or help. Often they are paralysed by shock. The most dangerous moment is the 10 minutes to half an hour when you're being taken to the safe house. That's when the kidnappers are most volatile because it's when they stand the highest chance of getting caught. Just try to remember that if they had wanted to kill you, they would have done. You are worth more to them alive than dead.

"The chances are that you will be kept in solitary and you will be blindfolded whenever you come into contact with one of the kidnappers. This is partly to make sure you can't identify them, but also to help them see you as a commodity rather than a person. It becomes much harder for them to treat you badly when they see you as a human, so you should always be trying to connect with them. Ask them for what you need – medicines, newspapers – but don't push them. And eat what you're given. You never know when your next meal is coming. And above all, don't try to negotiate your own release. You will screw things up big time. Trust that there's someone like me negotiating for you."

And when I'm released? What kind of state am I likely to be in?

"There's been a lot of research into this. But my experience is that people generally come out in much the same shape as they went in. If you're psychologically well when you are taken, then there will be no long lasting damage; if you're not, there might well be."

That's not good news for me, then. What about Stockholm syndrome? Is there any chance I will fall in love with my kidnappers?

"None whatsoever. That case appears to have been a one-off – a perfect storm of two compatible personality disorders between kidnapper and hostage. I've never known it happen in any case in which I've been involved."

Which just leaves one last important question. How on earth does one get in touch with an anonymous hostage negotiator when one needs one?

"Your insurance company will know where to find me."

I don't have one for kidnap and ransom.

"You should if you move somewhere dangerous. Or, failing that, you can get me through a security company. Try Compass Risk Management."

You know what, Ben? No insult or anything, but I rather hope we don't meet again.

"Me too, John. Me too."

• The Negotiator by Ben Lopez is published by Little, Brown, £17.99. To order a copy for £13.99 with free uk p&p, go to theguardian.com/bookshop or call 0330 333 6846.

• This article was amended on 15 August 2011. The original sub-heading said that Ben Lopez has spent 17 years bartering with kidnappers. This has been corrected.