It seems as though you are not familiar with the file sharing. First of all, bittorrent is a kind of wondrous invention, probably based on chaos theory :-)
Basically, if you have a TV station that has an antenna (emitter), you can add many more TV receivers in the area all around the emitter. On the internet, on the other hand, it is not possible to add more viewers without building more infrastructure that includes cables and servers.
By using bittorrent protocol, the content can be distributed, scattered in a very large number of small pieces that are everywhere, stored on many different computers. This way, we can add capability to the internet itself. The downloads are summing the upload speeds of many people, so its also fast. However, bittorrent protocol also features trackers, server programs that announce the existence of files and channel the searches. There are many trackers that anyone can add and maintain, and many communities, forums, web sites, search engines and so forth.
The Pirate Bay is the most famous of all bittorrent search engines that features its own tracker and a forum. Up to this point, there is no reason why any of this would be illegal or detrimental in its essence. TPB is actually, famous for the "pirates" and the community/voters who check torrents and spot viruses, hoaxes and stuff like that.
The important thing about the particular torrent file you are looking at, is that it is mentioned at TPB site rather than at some bad site, that it is properly documented with an info file and commented by the downloaders. The second important thing is of course, the file safety - that it is not a virus program (e.g. some .exe file).
Finally, whether the file is legal to own, watch, or give to your friends is completely unknown. This is because such information is not attached to the file in any possible form, other than its proper name, description and creator (which satisfies the bare minimum). The only remaining possibility is that you actually find the department at the BBC Four that is at all willing to announce the legal status of this file and ask them for their word on it.
Since many years passed since I had to travel to Britain for two days only to watch this documentary, the last known message that I saw was that it was public like a public TV program, but for Britain only by internet (presumably to limit the load on their servers). So, it is possible that you should not see it if you live in any other country. Maybe you can download it, but it is unlikely that there will be any official approval that says that you may visit TPB for any reason whatsoever. That is wrong for anyone to say in general, so this issue simply isn't regulated, because perhaps it shouldn't be regulated per se, in such a crude way. Its maybe subject to smaller-scale private regulation and checks.
I think that the documentary film should have an honorable mention on this site: there should be a post with all the information included. Unfortunately, internet movie database does not have as much information as TPB has.
http://www.imdb.com/title/tt1674741/?ref_=fn_al_tt_1&licb=0.8408335313450691There are about 15 people on the planet involved in the sharing of this file. Lets check info and give the documentary some credit.
Chaos theory has a bad name, conjuring up images of unpredictable weather, economic crashes and science gone wrong. But there is a fascinating and hidden side to Chaos, one that scientists are only now beginning to understand.
It turns out that chaos theory answers a question that mankind has asked for millennia - how did we get here?
In this documentary, Professor Jim Al-Khalili sets out to uncover one of the great mysteries of science - how does a universe that starts off as dust end up with intelligent life? How does order emerge from disorder?
It's a mindbending, counterintuitive and for many people a deeply troubling idea. But Professor Al-Khalili reveals the science behind much of beauty and structure in the natural world and discovers that far from it being magic or an act of God, it is in fact an intrinsic part of the laws of physics. Amazingly, it turns out that the mathematics of chaos can explain how and why the universe creates exquisite order and pattern.
And the best thing is that one doesn't need to be a scientist to understand it. The natural world is full of awe-inspiring examples of the way nature transforms simplicity into complexity. From trees to clouds to humans - after watching this film you'll never be able to look at the world in the same way again.
Airtime: GMT 10:00pm
Airdate: 14/01/2010
Duration: 0:59:15
A/R (WxH): 1:1.78 (720x400)
VCodec: XviD (2 pass MPEG)
ACodec: AC3 2ch 192Kbps
Flawless encoding
Pls. help seed to keep torrent alive.
I also mentioned the Deluge bittorrent client program, because it is open source and free, so I wouldn't like to leave the users accidentally bumping into any wrong download on the internet.