advice on crash responsibility

[Punkstig]

So from your extra info and picture, it looks like you were overtaking on zig zags

You're allowed to overtake on zig zags, it's the vehicle closest to the crossing that you're not allowed to overtake!

With regards to having discussions with their insurer-
It doesn't matter what the other party's excess is to you, they have agreed a contract with their insurers, you have agreed one with yours!

If they have disclosed they have a witness then legally they have to send you a copy of their statement!