In a private sale, I'd expect, even at a quick glance, a car of that type, mileage and spec to far exceed £12k.
There are many free sources to use as a yardstick as to how much your car might be worth.
Here's my tried and tested method and it usually is 'on the money' (has been in my experience anyway)...
Free Used car valuations for Trade, PX, Private and Retail can be had on the following websites:
Wisebuyers UK
What Car Used Car Valuations
Parkers Price Guide Used Valuations
Glass Used Car Valuations
What I do is get a valuation for private, PX and/ or retail price off each one and note the valuation down from each site. Total them and divide by 4 to get the avergae across the 4 valuation sites... Longwinded like me but accessible 24 hours per day, free and legal.
Remember, that's just a suggestion and it's only a guide!
Another free source is this Ford PX pricing link:
https://www.capconnect.co.uk/ConsumerValues/Ford.aspx?CH=PWRTZAlso, if you sign into Autotrader and start the process off as if you are going to sell your car with them, the website, on receipt of your registration number, will suggest a price for you to advertise the car at, based on other vehicles for sale on AT.
Hope this assists someone...
Cheers