Again, from conversations on other posts, it seems that Google is informing some owners on Google Webmaster Tools that they have detected a 'dubious' linking profile - I can't recall the exact message, but I understand that if this is the case, there is an option to submit a list of the linking sites you think might be 'dubious', with a disclaimer that you did not invite these links.
If no such message is showing on GWT, chances are that G has just devalued these links, rendering the site less relevant in the Google index, in which case a fresh, targeted link-building campaign would perhaps be the most immediate task. There are experts here with much more experience than myself, but I would suggest local, national and industry-related directory sites, links from authority supplier sites ( reciprocal if necessary ); check the backlink profile of the competitor sites on Page 1 for your targeted terms ; generally run searches for every phrase you might want to be listed for, make a list of those which are non-commercial and non-competitive ( Yalwa, Qype, Yelp. Brownbook, Hotfrog, Tuugo, YourLocal etc ) and create entries on these ( some of which are pretty much micro-sites ).
Oh, and most importantly, create a Google Places account and go the whole hog on completing all of the options - photos, opening times, contact details etc. I didn't catch your location, but if you run a search on google.co.uk for 'jewellery in liverpool' ( I'm a 'Pool fan, Wembley here we come! ), 'jewellery in lancashire, or any other location , you'll see that Google presents it's Google Places results at the top of SERPs, most of the time. This will at least help with your local marketing, while links from respected directory sites should help your UK-wide and global reach.
It's a real kick in the teeth when you've relied on traffic from search terms on Google which have delivered for years, and then suddenly disappear, I feel your pain. I hope you find enough good advice from the experienced bunch of people who contribute to this forum, I certainly have.