It seems as though 'cashing in your family jewels,rolex watches and any type of gold' are becoming big business, since the recent financial saga.We have been getting leaflet drops for the last month or so, usually with a mobile phone number and 'instant response' for valuation. Similar with people setting up new stall or kiosk outlets.
Personally, I would stick with a reputable local outfit. At least you can take any items for a face to face encounter, and not wait for that generous offer.
A close friend of mine owns 3 jewellery shops and he told me that any 'diamond' ring under £500 has a stone of little value; you are paying for the intricate mount which is fashioned to bring out the best in the stone. This is the reason that many people are disappointed when trying to cash in rings as value is only given for the scrap gold which isu usually a third of the weight of the metal.