Car being written off - help needed to maximise claim

My wife has just been involved in an accident where her car looks as though it may well be written off (contacted by garage yesterday who state that the final decision will be with the insurance companies engineer tomorrow). Anyway, the other driver has admitted responsibility and is being prosecuted for due care so my wife is totally blameless (she was lawfully parked at the time).

My wifes car is a 2003 53 plate Fiesta 1.4LX and looking at dealer forecourt prices will cost between £6,600 and £7,000 to replace like for like with the exact same model. Trade price (which is what we expect to be offered is around £5,600. I have already started collecting information from dealers and newspapers in relation to the price it will cost us to replace it and intend presenting this as evidence if the offer is rubbish.

I have a reasonable idea of how to deal with the insurers offers but there will obviously be a point where the insurers tell me to take it or leave it:( .

I would welcome advice from anyone in the insurance industry or from anyone that has been in a similar position previously and had a reasonable settlement re the best way to approach this. All we want is to be left in the same position as we were prior to the accident and not to need to shell out any money to replace the car with one of the same. The insurers so far have been great - providing a replacement car within 3 hours of reporting the accident but I have a feeling that we will come down to earth very quickly when we receive that first offer!