Written off simply means “beyond what the insurance co consider economic to repair” not that it’s actually beyond repair.
Unfortunately, a 12yr old car is well beyond economic repair given that even in good condition it’d be a few hundred quid at most if you sold it. £1100 actually sounds like quite a good deal from the ins co.
Maybe try and get a bit of a rise out of them – perhaps claim costs of a hire car necessary for the time you’ll be without a vehicle but realistically I’d just accept it. You’ll have trouble selling the car on or insuring it if it’s got “write off” against it on the insurance database.
I had the same when my old Ford got written off, the ins co actually gave me a very good deal on it. So good in fact that when my local garage heard how much I’d got for it they told me to take the payoff and run quick before the ins co found out they’d put one too many 0’s on the end of it!