I find the Rank Tracker tool really useful for this. Put in the keywords you are interested in then tick "track history". It make take a while for things to change but you can see what has happened. You are also not restricted to the weekly ranking update so you can do it now and capture the current rank of your old site before launch.

What are peoples thoughts and ratings on SEO agencies in London. There are so many of them it is hard to understand which are the best.

On the BItly examples I've seen although the link says bitly.com the referring has a domain of t.co. Have you looked to see if there are any from t.co?