I don’t know if you have reported this to police but you should do. It will give them something to do! I spent far too much time with people dropping litter parking on double yellow lines and speeding and drinking tea.
Don’t be fobbed off that this is a civil matter. This is intentional criminal damage.
Don’t speak to them on the telephone, turn up at the police station. If they try to tell you it’s a civil matter, tell them you have already spoken to a solicitor and you have been told by the solicitor that the police would say that and you want this guy prosecuted.
In addition, you can of course take the matter to the Small Claims Court if you wish although if the guy is prosecuted successfully, the court would normally award compensation in your favour against him.
How much? Believe it not, not a lot. Although having said that, I don’t how much Wisteria Bush costs. It would be the costs of getting a mature Bush and having the dead one removed and the new one planted. I imagine that small bushes are relatively cheap but mature ones more expensive. You would probably be looking at a few hundred pounds I would imagine but I am not a gardener but overall the intention is to put you back in the position that you would have been had this incident not occurred.
With regard to stress and inconvenience, I’m afraid that you really need to write that off.