'My job is betrayal'

What sort of person strikes up a close friendship with someone over several months, only to betray them, and expose them?

Jaspal Singh, who led a team of undercover reporters to expose the network of criminality surrounding illegal immigration in the UK, does it for a living.

Every covert operation is a betrayal, and not everyone can handle it.

I've been doing this for more than 10 years, building up relationships with criminals over six months or more, even up to a year, and there are only a handful of others in it for that long. Most people can only do it once.

I don't know how I handle it. You can use devices, convince yourself the target deserves it, but at the end of the day you have betrayed a human being and it's a question of whether you can live with it. I can.

HOW THIS STORY UNFOLDED Trade in fake documents for illegal immigrants uncovered as part of separate story South Asian community in Southall, west London, penetrated via a tried and trusted contact, the "fixer" Fixer sounds out members of community as sources Sources provide way in, giving intelligence and names of potential targets Sources protected by never meeting or being introduced to targets with reporters Information checked and double-checked - for example, fake document samples inspected to confirm trade exists Houses visited by posing as employer looking for worker accommodation

You have to start by knowing what you're looking for. There's a lot of painstaking work in identifying targets and places you want to film to provide evidence for your story.

After the first series of meetings with a target, building up trust - the trust you'll eventually betray - you can start filming, provided you have sufficient evidence.

It's all very strictly controlled with every bit of filming having to be justified and scheduled, but even after 10 years I still get the jitters when I arrive at the location, check my kit a final time and call in to the support team to say I'm ready to go.

But then as soon as I'm in, I relax. I'm playing a role. The guy has an assumption I'm a dodgy geezer, and part of me is thinking I am a dodgy geezer.

I've learned to forget I'm wearing the kit, though part of me is always thinking about making sure I get the shots.

I'm always tuned in to the slightest unease, and you know if they're suspicious because of the questions they start asking. Then, put yourself in their shoes - they're the nervous ones - so turn it on them and act affronted.

If it goes beyond that you're in big trouble; you've done something very, very wrong. The closest I've got was being lightly patted down, but I pretended it tickled and they found nothing.

IF YOUR TARGET BECOMES SUSPICIOUS... Become aggressive - and indignant - all the time making way to exit, aiming to link up with support team Take out cigarettes, offer them one - most smoke - and light one yourself Use your lit cigarette as a barrier, jabbing it towards them as you speak - puts them on defensive

We have an exit strategy for stepping out of these relationships, to protect the fixer and sources, and put some distance between the reporter and target before the exposure.

I don't feel sorry for the criminals afterwards, though I did feel sorry for the "faujis", the illegal immigrants, on this story, and they feel sorry for themselves - a lot of them have gone into a situation they never imagined.

The exit strategy is one of the essential elements for a successful covert operation, along with colleagues you can rely on, good kit, preparation, and sticking to the plan.

But to get in with a criminal he's got to like you; to stay in with him you've got to become his friend; and to do business with him he's got to trust you.

Then you betray him. That's really what I get paid for.

The undercover reporter's name has been changed and his picture changed to protect his identity.