The homeless man turned bestselling author on how his cat saved him from drugs, and why Bob thinks he's human

In last year's bestselling book, A Street Cat Named Bob, you say that you and Bob saved each other. It's an inspiring story. How did you meet?

Bob turned up at my flat one day and, after he'd been sitting on my doorstep for three days, I invited him in. He had a leg injury – he'd been attacked by a fox – so I had him treated, and I tried to find who he belonged to but nobody showed any interest. We just had a connection. He kept following me around, and it became natural for us to stick together.

You've just adapted the book for children. Some children's books – The Hunger Games, Philip Pullman's titles – are pretty dark, but not many deal with heroin addiction. How have you made it child-friendly?

Well, we've taken out the really dark stuff, but we've also tried to make the audience aware of the dangers of a particular lifestyle, while giving them an understanding of why people go down this route. Hopefully it will deter people, but also make them more aware of the issues – how drug use can provide an escape for some people. I think it's well balanced for 11 and above, which is the age group it's aimed at.

So you got over heroin and methadone addiction, in part thanks to Bob, but how did you become homeless, and why did you start using heroin in the first place?

About 10 or 11 years ago, I was sleeping rough. I thought it would just be for a few nights, but it was for a couple of years. I became homeless because I was staying with my sister, and I didn't get on with my brother-in-law. I was a teenage tearaway goth, I was very angry, and my sister and her husband were raising two children, and it was probably a bit too much having me hanging around. I had to move out and I slept on sofas and floors of friends, but you wear out your welcome pretty quickly and eventually run out of sofas to sleep on, so you end up sleeping rough. Once that happens, getting a job becomes a problem – the minute you become no fixed abode you become invisible. I started to slip into depression and drugs were a great way to escape. They were all around me so I tried it and found out it was pretty nice. Or rather, nice when you're doing it. Coming off it is another matter.

The representation of heroin addiction in films and movies suggests it benignly resigns you to whatever life throws at you. Is that something to do with its appeal when you're sleeping rough?

In a way. But it traps you. Heroin is a great excuse to stay on the streets and do nothing about your life. It's definitely glamorised in films, but it's an easy option – although you do have to go shoplifting four times a day to fund your habit.

You were caught shoplifting in Marks & Spencer in Islington…

I was. I would dress smartly, go at lunchtime when it was busy and load up on meats and whatever; maybe a shirt from upstairs. Then I'd go down the pub and sell them at half the price. That's how a lot of people feed habits, from stolen goods. Unfortunately, when you get caught, you end up in the prison system and it can make some people worse. I got put on drug rehabilitation orders and probation, but I never served a sentence. It was Bob who gave me the determination to knuckle down and get over it. Using drugs is a selfish thing; Bob gave me something else to focus on.

As you mention in your book, there are a lot of homeless people with dogs. A dog will stick with you even if you can't feed it. With a cat it's a much more equal relationship, but do they offer as much companionship?

We're definitely equals. In fact, he's the boss of me if anything. Where I go, he wants to go. If I don't take him somewhere, he gets a bit antsy. Dogs do provide security on the street but often people don't train them properly and they will go for you.

Why is he called Bob?

When I first got him he hadn't been neutered. One minute, he was all sweet, the next he would go for me. I was watching the box set of Twin Peaks at the time, so he's named after Killer Bob/Leland Palmer. It suits him.

You claim in your book that you could tell immediately that Bob had personality. What do you say to people who say cats don't have a personality, they're just furry sociopaths?

I say they obviously don't know cats. If you've ever lived with a cat, you'll know they do. Bob is loyal – the few times I have slept rough with him, he stayed with me. He's faithful to the core. Cats think for themselves. Bob opens cupboards when he's hungry – I have to put child locks on the fridge…

Exactly – cats are basically land sharks, always thinking about food. If he was big enough, Bob would probably eat you…

Bob would never eat me – look at him, he's just so relaxed. I get complete adoration from him. And he thinks he's a person; he doesn't realise he's a cat.

Is it true that the Hollywood agent who brought Marley & Me to the big screen is in talks about turning Bob's story into a film?

He's touting our book around, yes, and we've had a few initial offers. It would be incredible to see it on the big screen. It's looking more likely every day. It's crazy but, having been No 1 in the books chart for coming up to a year now, it's a possibility.

Will Bob play himself?

Who else could play him? He's such a character. Plus, it's not like you can train them; cats do what they want to do. You can't make them do anything.

How is he adapting to his celebrity status? Are you worried he might turn into a bit of a prima donna, like Cheeta the chimpanzee did following the publication of his book, Me Cheeta?

He's already a little bit of a diva. He's definitely demanding more treats and he likes to work fewer hours – he's very vocal about it. But he's the boss, so if he says it's time to go home, then it's time to go home. He won't be running off with Jennifer Aniston, will you, Bob?

He is very handsome, and I know people have tried to buy Bob from you. Are you worried the original owner will reclaim him?

He's my owner. And there's nobody else who could ever claim him. We've been together for over six years now. If someone came forward now, I'd tell them where to go jump.

If you become rich and famous, what will you do with the money?

Make sure our lives are comfortable, and we never have to worry about sleeping rough again.

Bob: No Ordinary Cat is published on 14 February by Hodder & Stoughton