without pictures it's going to be very hard to give a realistic value on anything
condition is everything, even if it's scrap there will be parts on it that would make it have a certain value
if it's not breaking the rules your best bet would be to get onto facebook and look up a group called ford sierra appreciation club as there are a lot of people who restore cars there or use them as daily drivers and they would have a much better idea if your £1500 car is worth £1500 or if it's worth £1500