I knew it would all go wrong.
My insurance company says that because the car only has third party insurance (that's all I was offered because it's over 25 years old) there is no legal assistance included. This seems to mean that they are unwilling to talk to the other insurance company on my behalf. My brokers said I should talk to my car club (AA type equivalent) who do provide legal assistance. My car club said I would only need legal assistance if the man who ran into me contests the claim and even then only if there is any real doubt about his culpability and that my insurance company should deal with it.
So the car club says it's not their problem and the insurance brokers say it's not theirs.
I went to ask the Guardia Civil (traffic police) what I could do. They say the insurance company has an obligation to pursue the claim on my behalf and if they won't I should make a "denuncia" - a sort of official complaint against them.
As you can imagine these are all pretty difficult conversations in my version of Spanish!