Looks like the real reason behind Interflora’s unfortunate penalty is “advertorial” links. A lot of theories are out there but here is solid evidence.
Look at these advertorial links:
And below is an excerpt from a blog post published by Matt Cutts, although Matt doesn’t refer to Interflora at all. The statement makes perfect sense if you take into account some examples highlighted above.
“Google has said for years that selling links that pass PageRank violates our quality guidelines. We continue to reiterate that guidance periodically to help remind site owners and webmasters of that policy.
Please be wary if someone approaches you and wants to pay you for links or “advertorial” pages on your site that pass PageRank. Selling links (or entire advertorial pages with embedded links) that pass PageRank violates our quality guidelines, and Google does take action on such violations. The consequences for a linkselling site start with losing trust in Google’s search results, as well as reduction of the site’s visible PageRank in the Google Toolbar. The consequences can also include lower rankings for that site in Google’s search results.”