Q.What is happening to my Wisteria plant?
I have a Wisteria plant in my back garden which I planted from pot about ten years ago. It grows on a pergola along with an ivy, Clematis and a few roses. It flowered beautifully this year, but since then, there has been no new growth, no new shoots or leaves, and the leaves which are already present are turning yellow/brown and falling off. It gets plenty of sunlight and water, has no root rot and no damage to its trunk. It seems to be dying and I was wondering what is wrong with it. (We did have some late frost this year, but surely it should have recovered by now?)

I would check for crown or root galls. It sounds like something is choking the plant and galls would do that. Here is some information on them that may be healthy:
http://hortsense.cahnrs.wsu.edu/Search/MainMenuWithFactSheet.aspx?CategoryId=12&ProblemId=4002