Not a single bubble seen through the locks on the plum for a week, so have moved it to the cold cold garage to try to ensure the yeast dies completely. I'll give it a week then taste it. If it's nice (enough) I'll bottle it, else I'll rack it with perhaps some chemical taste adjuster - probably chalk (or potassium carbonate if I can get some locally) and leave it to mature a bit longer in demijohns.
The elderberry's bubbling is slowing now, only about 1 a second instead of the 2+ it was doing.
Can probably rack that in about a week.