Following up to myself...
I haven't yet decoded the tape (if it says
anyhthing at all). Luckily I
just got _Computers and Typesetting_ which covers plenty of obscure
typesetting codes (which is the only area I know of in which six-hole tape
ever became popular).
It's called _Computer Peripherals and Typesetting_. Everything else I said
about it is right (copyright 1968, written by HMSO). Incidentally, the
price is given on the copyright page as ?8 0s. 0d. net.
-- Derek