Or alternately, Facebook sent the images to the police because the police are the next step in the chain. Facebook passed the images (rightly or wrongly, but from the sounds of it because it was user comments that made the images become porn - which is a whole further debate). Then the BBC sent them those images and said they were illegal. So Facebook forwarded it on to the police and said we have this report, we're doing our duty and involving you. Which I think is fair. I have nowhere found anything that shows Facebook were trying to shop the BBC to the police. Getting the police involved is probably a very good idea at this point.
Facebook isn't a person either, who will necessarily do all the joined up thinking and make special exceptions. They're a colossal company with a lot of procedures and policies. Someone flags an image up, policy says someone looks at it and makes a decision. Probably the poor sods have to look at unsavoury images one after the other and they're going through high volume saying: "naked child - ban; ordinary beach picture - pass." They probably can't really go through all the comments and say "well, I think it's an ordinary beach picture but someone further down has posted a comment saying "wow - hot". They're neither police nor lawyers and even those parties would be going back and forth through a lot of grey areas. If another fifteen year old (and let's remember fifteen isn't paedophilia) says "hot", it's a pass. If the comment is from a forty-five year old man, you classify the picture as porn? If the picture is in a collection of ordinary photos without comments, it's a pass, but if the collection is nothing but fifteen year old girls, you ban the image? This all sounds really, really hard and grey. That's even when you accept that adding a comment from a stranger turns your family holiday photo from a family holiday photo to porn. So it may well be that images were passed. Apparently only one picture was unambiguously pornographic and even then without seeing it (which I would far rather not), I'm willing to give Facebook some benefit of the doubt knowing what the BBC can be like from personal experience.
So that's one side of Facebook and their policies. Another side of Facebook and their policies probably say something like "if someone emails you and says 'here is a load of child porn', then refer it to the police immediately". I doubt their policy says something like "if someone emails you child porn then decide for yourself whether you feel like reporting it.". Remember - Facebook isn't a person. Some person watching a series of images on one side of the company and passing them according to company policy isn't the same person or next desk of someone receiving an email saying "I'm sending you child porn". I think people may be ascribing to Facebook a sort of personhood and accompanying nuance that isn't really appropriate for a giant corporation. Bringing in the police seems absolutely the correct thing to do to me. The police can say whether something should be taken further, consider context (i.e. the BBC are probably not a paedophile ring - at least now that Jimmy Saville is dead). It's not like Facebook are attempting to stitch up the BBC which is how the BBC seem to be trying to cast it. The BBC were trying to create a story. I mean, it's the BBC - that's their purpose is news and stories. This wasn't some helpful journalist acting in a private capacity to stop child porn.
So despite the emotive nature of the subject, I'm actually with the poster that called this an "own goal" for the BBC. For those who read superficially and do not consider, I'm sure the BBC look heroic and Facebook evil and tolerant of child porn. But to the majority of people, it makes the BBC sound like they're trying to set themselves up as victims. IMO.