Below are some links to documents I scanned from my old junk pile, to see other things I found see this page.
Here is an overview of EPSS.
This is from 1977.
I think I got this on 'EPSS Open Day' There are some other documents EPSS with it that I have not scanned yet.
Here is an overview of some early UK packet switching networks.
This is about the early packet switching networks in the UK by P.T.F.Kelly B.Sc.(ENG.), C.ENG., M.I.E.E., M.B.C.S. (apparently you were in trouble if you missed out any of these initials).
It is from the October 1981 edition of the Post Office Electrical Engineers Journal (IPOEE 75th anniversary edition).
Here is an overview of Euronet
From Post Office telecommunications journal Autumn 1979 an article by D E Hadley and A C Barnes. (Two authors but not as impressive initials as P.T.F.Kelly B.Sc.(ENG.), C.ENG., M.I.E.E., M.B.C.S. and a slightly more down market journal).
On this page are some articles from Computer Weekly about these Post Office/BT networks being introduced.
On this page is an article from Network Magazine April 1986 about what big business X.25 is at that time.
Other PSS related pages