Today i had a meeting with the council enviromental officer (the supervisor of the person that done the damage) and a representative of the manufacturers of the weedkiller.
I now know the weedkiller is called Touche.
It's 2 main ingredients are GLYPHOSATE and DIURON.
The council man said it was a contact herbicide, yet the rep of the maker said it was contact as well as systemic herbicide.
Now i am confused, i thought it had to be one or the other...not both?
They both refused to take responsibility for the damage, they said Drift had not caused them to die.
Just for my own peace of mind i took the liberty of recording this conversation today. I did not tell them i was recording it.
It seems the only way i am going to get close to resolving this is to have some of the conifers analysed, but even then they might say it wasn't their man that done it.
Is it worth dragging it all through the small claims court, or is that the approach they want me to take, and just dont bother.
This council is renowned for not admitting to anything they do wrong.

I really dont know what to do for the best.
Thank you for all the supportive replies, it's very much appreciated.