I drew up the following chart using data from the Met Office National Climate Information Centre HadUK-Grid climate data.
We have seen long-term average temperatures increase, in England since the 1960s, with the 30 year average increasing by 0.5 degrees Celsius (see Central England Temperature with Climate Change Projections).
In this graph you can see how the lower extremes have changed. The number of days with an the air temperature below freezing point (an ‘Air Frost’) have decreased from a 30 year average of 53 days per year, down to 43 days per year. This trend is set to continue. And it does affect what plants – as well as pests and diseases – are able to survive our winters.