Any advice/help is much appreciated. We are not sure whether our plum tree has a case of bacterial canker or whether this is just simply excess gum production due to some bad pruning.
Yes it could be, cut back to healthy wood. But leave it until the Summer Month's. It will also avoid silver leaf doing so. Another sign of canker the leaves will take on the appearance they have been peppered with a shot gun as time goes on
I failed to mention you'll need a wound paint after pruning