Does a Victoria Plum Tree loose all it's leaves in winter ?
This depends on your climate zone, but typically, yes it does. This process is necessary to give it a rest for next year's fruiting.
Is the resulting fruit from the Brompton rootstock edible. What is it most suitable for?
Yes, they would be edible, but not likely be a very tasty Plum.
why has my tree produced hundreds of plums covering every branch and breaking many branches the fruit would be the size of a wallnut
Victoria plum trees are biennial fruiters, which means they tend to have a very small crop one season followed by a bumper crop the next. It sounds like you're in a bumper year. For now the best thing to do is try to keep up with picking the fruit. In future years when you see a lot of fruit starting to set, go through and remove about a quarter of the fruit when it's very small (about pea sized). This will make the remaining fruit bigger and save the branches from breaking. You can read more about Victoria plums here:
Can you prune a Victoria plum tree now when flowering? Or prune after flowering in May onwards?
This article will help you.
This is a four year old tree. It has produced tiny plums in the past, but none have ever matured; they drop off. We had it pruned for the first time in February; it blossomed and looked beautiful and we hoped that we might actually have fruit this year. However, it is looking unwell now. There are no visible spots or marks on its leaves but they are limp and droopy. We placed a manure-type compost around the bottom of the trunk in March. Do you have any idea what could be wrong with it?
It is most likely Peach Leaf Curl. This Fungal infection will also infect plums. This article will help:
My Victoria Plum tree leaves are turning red with black spots on them , curling up . Some of the plums are shrivelling up .
This looks like the disease Xylella Fastidiosa. This is caused, usually, by leafhopper insects.
There isn't really anything to treat the disease, but you can maintain the symptoms. This article will help:
This article will help you to care for the tree: