The Knack: How To Go Undercover

DITCH ANY ideas about Hollywood-style super-sleuthing. Undercover reporting is hugely corrosive in terms of your energy - it's exhausting. It will take time to get your subjects to think you're one of their own - it's a case of turning up in their environment and sowing the seeds very slowly. For example, with the football hooligan story, we'd heard that one of the subjects, Jason Marriner, was quite affable, so we moved into his area, hung around the same pubs and gave the impression that we were dodgy dealers. Eventually he felt compelled to say, "Who are you?" because he wanted to know who the new guys were on his manor and we took it from there.

It can be nerve-racking. I remember a terrifying journey to a football match in the company of a football hooligan called Nightmare - he wasn't quite sure about me and was boasting about slashing a policeman's throat within a foot of MY throat. You don't know what will happen if your cover is blown - when I was in Moscow filming a subject in a club, my camera equipment beeped when I went through the metal detectors; there were men with guns at the doors and I had no idea what could possibly happen. Fortunately, the company I was in and my photographer's jacket meant I was left alone.

It's important to get your details right. For the football investigation I nearly made a fatal error when I had a tattoo done - I had claimed that it was a couple of years old but I'd had a relatively new Chelsea logo done. I think that puzzled our boy Jason but it didn't actually spark an alert in him - we were very lucky.

Keep a firm sense of who you have to be in each world. Don't allow any of your subjects to imprint upon you - I find that if I treat the subjects on a very shallow basis then they don't embed themselves and nothing too much is left behind. I've had death threats but I'm being well looked after in a BBC safe house.

Donal MacIntyre's next investigation, into international fraud, can be seen on `MacIntyre Undercover', next Tuesday at 9.30pm on BBC1. His book, `MacIntyre: One Man... Four Lives' is published by BBC Worldwide (pounds 6.99).