Had another think about Christian's advice with the off terminals, and
rejected it - the original Randall did not support motorised off
valves, so I can't have those in my system (especially as it is so
old!)

You may have misunderstood. The purpose of the Off terminals is not
necessarily to drive motorised off valves. Many wiring schemes use the off
terminals for other purposes. However, I don't think it is the problem in
your case anyway.

http://www.danfoss-randall.co.uk/default.asp?strSearchResult=tem1019.asp?intPage=99 0|intLang=2|strLang=en|intLevel=2|intLevel2ID=990

Shows:

1 - Neutral
2 - CH On
3 - NC
4 - HW On
5 - NC
6 - L (in)
7 - N (in)
8 - earth

Now see if you can remember where the original wires went and it should be
obvious where to place them on the new programmer. If the room thermostat
still doesn't work, are you sure it was working before?

Christian.