Cheers Tim I suspected this was a result of this "Unnatural links to your site" and appreciate the reinforcement.
Ranking improvements were solid before unnatural links were put in place but I agree it is a combination of the two.
This just popped up in "Manual Actions" in Webmaster Tools
Google has detected a pattern of unnatural artificial, deceptive, or manipulative links pointing to pages on this site. Some links may be outside of the webmaster’s control, so for this incident we are taking targeted action on the unnatural links instead of on the site’s ranking as a whole.
I will get all the links removed to show best intent then click "Request A Review" hopefully this will speed up the process?
This was out of my control but certainly reinforces my view "Links are earned not bought!"