Chris Rogers (centre) is pickpocketed.

I am in Barcelona with my film crew and I am about film a gang of pickpockets. They are petty criminals who claim to be preparing for a crime blitz on the streets of London during the Olympic Games. They know we are journalists from the BBC and they are happy to be filmed. They haven’t even requested anonymity.  

I have often filmed criminal activity secretly and while undercover, but the editorial and legal aspects of such filming are nothing compared to the considerations around filming this kind of open access to criminal activity - and with good reason.

The BBC’s Editorial Guidelines are clear: when it comes to filming illegal activity, there has to be prima facie evidence of wrongdoing and filming it has to be in the public interest.

Even then, is there a compelling reason to film criminals at work? For example, do you need to film your own evidence to stand up your story? Is the prima facie evidence enough in itself to tell the story? Are you revealing anything new? And could it be illustrated in another way? Getting open access to criminals does not eradicate any of these questions: it makes them even more important. 

Early this year the Metropolitan Police made no secret of their concerns about organised gangs of pickpockets planning to target the London Olympics. While most journalists opted to cover the story by heading out on police raids targeting such gangs already operating in the UK, I wanted to get an insight into the criminal world the police were trying to shut down.

We conducted our investigation after informing both the British and Spanish police, and received backing from both. This was a case where showing the crime happening and explaining how it worked contributed directly to raising public awareness, and potentially to public security.

Many people have asked me how I get access to criminals. Earlier this year I also interviewed copper thieves. It's down to good old-fashioned, traditional journalism. You need to get off the phone, forget the internet and get out of the newsroom. You won’t find untold stories or decent contacts there.

We headed to Barcelona because there are more pickpocket crimes there than anywhere else in Europe. (OK, so the internet can be handy for statistics!)

In Barcelona we scoured the streets looking for pickpockets. Useless. They are so quick at what they do and they also mingle into the crowds, so the only evidence of thieves at work is a tourist looking for their handbag. We turned to local knowledge by asking locals for tip offs on who to look out for and where.

A cafe owner informed us he allowed gangs of Romanian pickpockets to eat at his cafe on the condition they left his customers alone. He introduced us to some pickpockets. The first few wanted money for their time but eventually we found a group which agreed to be filmed without payment.

As soon as we were filming, I asked them to agree on camera, for our own records, that they were happy to be identified, and warned them that the authorities, both in Spain and in the UK, would be able to see the footage. They didn’t care: the police already knew many of their names and faces. Getting caught didn’t bother them too much: in Spain, pickpocketing is only classified as a misdemeanour. The threat of the law doesn’t frighten them.

There you have it: nothing magical, but we had our gang of pickpockets. The reason why they volunteered became more evident when we filmed them a few weeks later. They are clearly proud of what they do; they see pickpocketing as an art, and a performance they have trained for all their life. They explained that it is part of their culture and family history. They are also fearless of arrest. Such is the speed of pickpocketing; tourists and police rarely catch them. 

Following the concerns over pickpockets announced by the police in the UK, there was a huge public interest and awareness argument that supported the filming of this gang. It enabled us to show what the police and, perhaps more importantly, also the public were up against and how they can protect themselves. But, even so, there are strict guidelines in place, and rightly so.

We could not aid or abet the pickpockets, and we could not in any way direct their criminal activities. Just filming an admission of a crime could result in a court order by the police for rushes, so all emails and notes have to be filed. We don’t yet know whether we’ll be required to handover footage. If we are served with a court order, it will be up to the BBC to decide how to respond.

We decided we would film the gang target a willing victim: me. But there is a fine line between making the public aware if how thieves operate and showing potential thieves how it’s done. We had to carefully consider how we filmed and edited the sequence of demonstrations.

Even though I knew they were targeting me, I didn’t feel a thing. It all happened so quickly, as they lifted my wallet from my back pocket and my phone from my bag. It became apparent that it would take years of practice and training to become an accomplished pickpocket.

We did film other pickpockets at work on real victims. With one of the gang we had already filmed advising us, we were able to stand in a public place and film other pickpockets in action. They weren’t known to our adviser, and they didn’t know they were being filmed. We don’t show the victims’ faces, but the pickpockets are plain to see.

We did this to confirm that our gang knew what they were talking about. It showed that their tactics not only work but are used by pickpockets everywhere. What we brought back from Barcelona was a film that provides a unique insight into these thieves. 

Investigative journalism is not easy - and there can be a minefield of editorial policy considerations. But there was never a time when I thought I should have opted for a simpler film, such as following a police crackdown on pickpockets.

Guidelines are there to make sure you serve the audience and the BBC responsibly. They are not there to stop you from conducting an investigation, which in this case served our audience much better than just footage of a police raid. We can offer an in-depth look at the tactics used by thieves who claim they can steal in just one second. I hope we will have saved many tourists from a disastrous visit to London 2012.

Chris Rogers' report can be seen on BBC TV News and is also on the BBC website.