Assuming you are in the uk (as question is posted in uk & ireland) yes by law you ARE obliged to return the vegetation to the owner - your neighbour. However,by putting the branches back onto your land,he is in effect giving them to you-making you the new owner of the branches and you can dispose of them as you see fit. BUT, as he sounds somewhat unpleasant it would only be your word against his if he were to get difficult if you were to dispose of the branches.
SO ;- you need some sort of video or documentary evidence to prove that he 'gave' the branches to you making you the new owner. Not sure whether the police could give you any sort of copy of the report, or whether any information in it would be applicable in proving this. You could - at risk of your greenhouse - put the stuff back onto his land, and hang around with a camera to record him returning it - then when you have this evidence,you could just burn the lot.
I wish you luck with this - neighbours and their chattels (whether animal, vegetable, mineral or offspring) can be sheer hell.
I know you gave a TD to the poster that said that you should consult an attorney, however; I would suggest the same. You need to protect yourself. One thing you could do is to send him a registered letter with a return receipt (proof that you sent it and he got it) outlining what you are going to do with the branches.
Say in the letter that the council told you to place the branches back in his yard which you complied with. Now that he has thrown the branches back into your yard, you are going to dispose of them. That should cover you but I would still consult a lawyer (which I am not) before you do this.
Because the guy is aggressive, I would not approach him personally.
I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.