Emma.
There is no way one can value your car without a lot more information, plus an inspection, plus a test drive. Sorry but "beautiful and really well maintained" is not enough. The value will depend principally on condition, age, mileage, and service history. I suggest you get it inspected by the AA or RAC, who are probably going to be the closest thing you can find to independant assessors without vested interests.
At 13 years old it is getting a bit long in the tooth, so be prepared to be disappointed by its value.