An update after some discussion over at StarDot...
It turns out the CPU card is a Control Universal EuroBeeb, which is a sort of cut down BBC Micro used for industrial applications. There was an application you could run to bake your own MOS ROM which allowed serial comms only; there also appears to be a BBC Micro ROM that lets you use EuroBeeb as a co-processor for the BBC via its serial port (I bet it is a bit slow!).
I acquired a copy of the ROM building application - it's a program written in BBC BASIC with various binary support files - and ran it on a BBC emulator. From what it says, you can configure EuroBeeb to just communicate via its serial port, which jibes with its use as an industrial control computer. No VDU card, monitor or keyboard required. So this means - perhaps... maybe... - I can hook it up to a terminal (via an RS232 line driver circuit) or a BBC Micro (RS423, which I think will be compatible without line drivers) and program it directly in BASIC (actually, BBC Basic II, which I think is already installed on the card).
One thing the ROM creation program does is allow you to specify a boot line in BASIC, which means I was wrong about it being in the battery backed up RAM.
The card's battery supports a RTC but there is corrosion evident. I am hoping that none of the tracks are zapped. First thing to do, then, will be to take the battery out, clean the PCB and continuity check all tracks. Then, check the voltage levels on the power supply. There is plenty of research still to be done, and I need to make a serial cable. What fun!
PS: it's this one -
http://www.eBay.co.uk/itm/181458750852