Unfortunately, iPlayer is indeed UK only unless you can find a UK based proxy that is fast enough.
Part 3 is currently on Youtube (but probably not for long: Auntie is watching...). Not actually about Kahn, but heavily featuring his archive's Autochromes. In 3-parts starting at: http://www.youtube.com/watch?v=nWeU5OexIls
It suffers from the usual first five minutes of telling you what you already heard in the previous episodes, but once you get past that it's fascinating.
I don't know how true to the original colour of the Autochromes the TV colouration is (which of course depends on what the Beeb does to it as well as how individual TVs display it) but to me the results as I see them are astonishing. The colour isn't strong or even very natural, but I find it very pleasing for the subject matter - perhaps along the lines of hand tinting.