Eric Thompson wrote:You can graft another plum onto that -- it's best to pick one that is a good pollinator match if you can, the the remaining branches may start fruiting better.
To graft, select one of the large branches and cut it, then do a "cleft graft" with another variety.
The lack of fruit may be from the variety (some ornamental plums are more flowering than fruiting), the pollination availability (if nothing compatible is nearby) or just the season and conditions (too cold and rainy for the bees when it flowers)
The grafting part needs a lot more detail than what I outlined, but it will be a fun project if you can research your way through it.
Thanks for your reply Eric! This is the first place I've lived that has any trees so I've plenty of research to do! You have given me a lot to think about, as the only other fruit 'tree' nearby is some sort of wild currant bush. In the two years we have lived here the tree has flowered before/around our last frost date so perhaps too early for pollinators. It is also Scotland, and my area typically has over 250 rainy days each year!
I still think it's worth a bash though so I will be trying to figure out what varieties might be a suitable match and then go from there, thank you! :)