This map will be of interest for gardeners in Europe as it gives the highest and lowest annual minimum temperatures. If you want to see more detail for your country click http://www.gardenweb.com/zones/europe/
The detailed climate zone map for the UK refers to -12c and it is true that up until the last two winters, the frequency of such low temperatures in SE England was very rare. However, winter 2010/11 has seen temperatures drop this low in many parts of England, including the South and East. Predictions are that UK winters could become even colder as climate change affects the flow of the oceans.
It will be interesting to see how this map changes over the next 50 years as Europe feels the effects of climate change.