My initial design did not include any means of fastening baseboard sections together. I hoped perhaps optimistically, that friction would do the job. One bump into the cantilevered end put paid to that. Given the presence of the baseboard support structure, a side attachment mechanism is required. I poked about in my favourite hardware catalogue and came upon table-leaf fasteners.
These latches are designed to drawn the two halves together which is perfect for my requirements. Upon belatedly referring to the Station Road Baseboards site to see what the accepted items for this job were, I turned up what looks like this very thing. The only downside is that the project out about a half an inch but I don’t see that as an issue.