The entirety of Britain has a cool, maritime climate (Koppen: Cfb -
Oceanic climate - Wikipedia, the free encyclopedia), and, despite Global Warming - this isn't about the change any time soon. While this generally means mild summers that are a mix of sunshine and cloud, chilly and very overcast (but not excessively cold) winters and regular but light precipitation year round (no dry season) - it is even more characterised by extreme
unpredictability.
This means that although this "martime climate" pattern is the norm over an average of 50, or 100 years - the climate varies dramatically from one year to the next - or even from decade to decade. Surely Global Warming and Climate Change are having an exacerbating effect but in fact the British climate has been like this for centuries.
So while generally you can expect mild to warm (but not hot) summers, and chilly cloudy (but not very cold) winters - this pattern is disrupted by cold snaps and heat waves and other types of "abnormal" weather. It is true that the last three winters have been excessively cold by British standards. But in fact it hasn't been cold
all winter.
Last year (2012-13) was actually quite mild during December and January. February to April were brutally cold and snowy. This was followed by a wonderfully hot dry summer - the first in about 6 years.
Another remark to make is that the weather in the UK is influenced by the fronts of the Atlantic Ocean as much as the season or time of year. A cold snap could descend from the Arctic any time from October to early May. A "heatwave" can occur from April to early October. Some years summer is wet and winter is dry, some years it's the other way round.
Part of the problem (and modern popular culture which is greatly influenced by America) is that even in Britain many people don't understand our own climate... and get stressed out/worried about these abnormal "snaps" of crazy weather. Actually climates like Britain's are extremely rare in North America (the only place which has anything even approaching it are parts of west coast Canada). Hollywood has led us to believe that summer should be hot, winter should be cold and snowy, spring should be lush and green and autumn a riot of colour and wind. This is the climate in the United States! It is not realistic to expect England to be like this at all - and the more you learn to love the unpredictability and relish in the surprises that the British climate can bring - the more you'll learn to love it.
(That said, I do think there is some truth in the argument that Climate Change is destroying/weakening the jet stream - which brings western Europe warm wet weather from the Caribbean and means that we are much much warmer than comparable locations at similar latitutes on other continents - ie. Labrador in Canada, or Eastern Siberia - giving Britain an even more unpredicable and at times, colder, climate than it had before)