My Grans cherry blosem tree has failed

There could be several reasons for this. When you say failed, how exactly? Did it blossom at all? If so, it could possibly have been frost that got it.

How old is the tree? If it is very old, they do die after a number of years. You might need to do some research on books in the library or internet.

Is it a small one in a pot? Sometimes, the roots get potbound and it eventually dies. If it is in a pot, again, the pot could have been frozen by the cold weather. I don't know what sort of winter your gran had.

If its leaves are looking sooty, mildewy, black or spotted, these are viruses and diseases. Again, we need more info.
Pruning should only usually be done to cut out diseased branches and after fruit has been picked.

Sorry couldn't be more help at this time.

Hi! Yep, found the book! It says ornamental cherry trees live for about 30 years. It did say that this process has been accelerated by outbreaks of disease, which are manifest by a general decline in vigour, a lack of flowers and a gradual dying back of the branches. No one seems sure of the cause, althought it appears to be a bacterial attack of some kind. It is apparent that the trees do not recover and the author advises any gardener facing this problem to replace the cherry tree with something different. He lists these as trees for a small garden. If you want me to do this, let me know and I'll pm you, as it comes from a library book. :-)