What exactly happened with Interflora?

For those of you who haven't heard about it yet, Interflora is a popular UK online shop for flowers and bouquets. Not long time ago it was on top positions in Google for keywords and phrases like 'flowers', 'flower delivery' etc. At the end of February the site lost its positions not only for these keywords, but for its brand name too.

Google said that they won't comment on the case, and SEO community started guessing what may have caused the penalty.

In the meantime Matt Cutts from Google's Web Spam team tweeted this: