Q.Patio plum tree
Hi I wonder if you can help I bought a patio plum tree since potting up it has never produced even a leaf on branches it only seems to have a leaf at the bottom of the main trunk can you help please,look forward to hearing from you,mike

Check the branches. Do they snap off and break or are they pliable?
The lower leaf you mention sounds like it is likely coming from the root stock.
My guess is that the tree died and the root system still has some life in it.
Check with the grower. Most reputable sellers will replace a new tree for one year.