Bit torrents also called "peer to peer" are where lots of pcs that have the data on them share in resending it to others requiring a copy, thus sharing the load. It means opening your PC to access by other people's computers.
BBC iPlayer works like this and is totally safe, but others may be more unsavoury. I tried it once with another vendor and got nowhere. The advertised film was nowhere to be found and lots of junk came down.
POSTSCRIPT: I've found this by the BFI:
Synopses
SLOW TRAIN TO RICCARTON
Library Synopsis
Documentary on the closure of the Hexham to Riccarton Junction railway line to m ake way for the Kielder Reservoir.
http://ftvdb.bfi.org.uk/sift/title/350168?view=synopsis
They suggest its in B&W. Is it only ten years old?
Not muuch more info I'm afraid. It doesnt seem to be available from them.
PPS
Have you searched Youtube?
http://www.youtube.com/results?searc...riccarton&aq=2
In particular the BBC's own channel?
http://www.youtube.com/user/BBCWorldwide