Trade in value of 2006 Peugeot 307 for Peugeot 308

I have a 2006 Peugeot 307 Zenith (metallic) with 17,000 miles on clock. Roughly what should I expect to get for this car in trade in for new Peugeot 308 same spec

Used to deal with account for company cars and was always amazed how much could be gained by ringing around a few different garages. Some can vary quite a bit. Its a few years ago now but I never found the Car Salesman's Guide (trade booklet) too useful. Try ringing a few different main dealers and don't forget to mention any knocks or scratches.

prob about 12k