I had the same thing when my ST was writted off back in november last year, the insurance took so long faffign about over liability that i didnt get a settlement until march this year, the first valuation they offered was way low and obliviously rejected, i backed this up by printing off adverts from autotrader etc of cars with a similar spec and age to what mine was ad told them that i wouldnt accept an offer lower that what i could buy another one for, after another daft offer they gave in and i was only about 200 quid out of pocket on the value.
took that money and bought my coupe, happy days.
They still haven't accepted liability officially yet but the lad who crashed into me is in court in a few weeks time charged with careless driving so hopefully once that is out of the way they will put an end to all this stupidity, not a quick process, as my crash was in november and its now september the following year.