my experience with insurance companys are they allways start with a low settlement figure because they expect you to want more,
they will have a figure which they wont budge on, you have just got to get as near to this as you can
another thing is the dealers profit, we all know every dealer has to make it, but your insurance wont pay it, as this is not the value of the car so their price will reflect it
try not to use solicitors as you will have to pay them even if the outcome is not what you want
insurance companys have lists of solicitors they will use who are experienced in this very thing
why not try to tell them you were selling the vechicle prior to the accident and had a serious offer of £18000 ,im sure you can show a few adverts, offers, etc
glad youre ok
good luck!