The ROM Plus is a ROM Board from Britannia Software Ltd. It also features a cartridge slot (which never became a standard).
Britannia ROM Plus
Review 1/2 (ACU, 4/1986)
Review 2/2 (ACU, 4/1986)
Advert (ACU Nov 1985)
The Rom Plus, open
The Rom Plus, plugged in
Boot message
Another shot
Top board side
Connector