Well I know he wont admit any liability because he doesnt know how it started and if he did then his own insurance could come after him as well
This makes me strongly suspect your friend hasn't given his insurance details to his neighbour's.
For your friend, that would come under the heading 'accepting liability'.
And, nine times out of ten, that would have been the end of the matter.
Going to court is pricey - most people would just hope their insurance covers it and let it go: higher premiums and all.
However, it looks like the neighbour's insurance company isn't letting it go.
Either they are refusing to pay out or they are insisting on your friend being liable.
If he had passed the insurance details on, this would all be dealt with between insurance companies.
The dispute would actually have arrived in the form of him arguing with his insurance company as to his liability.
The fact that it hasn't taken this form - and has taken the form of potential court proceedings. Undertaken by the neighbour or the neighbour's insurance company - suggests your friend did not pass his insurance details to his neighbour.
It also suggests that, if he went so far as to claim his own insurance for damage, he withheld information (that Fire Brigade incident report) from his insurers.
Though my guess is that he didn't notify his insurance company at all.
'Liability' isn't the same thing as consciously setting out to raze your neighbours' gardens.
I think his determination to avoid higher insurance premiums may well prove to be an object lesson in why you take out insurance in the first place.