Why is England so cloudy? Why, physically, some regions of the globe are affected by a noticeable cloudiness respect to others? Is the reason why some places are also rainy the same?
 A: Clouds are made of water. Not water vapor, but condensed water droplets. If the droplets grow too big, they'll fall down and the cloud disappears as rain. So far, that should all be familiar.
We can deduce that a few things are then needed for clouds to exist. Obviously, we need water in reasonable quantities in the neighborhood. The Gobi Desert has few clouds because it's  quite far from sea.
Secondly, that water has to end up in the atmosphere. That means it has to evaporate, which takes heat. But clouds are condensed water droplets, which means means that we can't have too much heat.
Britain is particularly cloudy because it's located in the Warm Gulfstream. The heat necessary to evaporate all that water was absorbed off the African American coast, and then transported along with the water. The air above Britain, on the other hand, is quite often coming from the polar areas and thus much colder. 
This combination of warm water flowing north and cool air flowing south provides the temperature difference that drives cloud formation around the British Isles.
A: This is an addendum to MSalter's answer.
If you look at a rain map of the UK (follow the link then select "Rainfall") it's immediately obvious that most rain falls in the west. This is because the air flow across the UK is predominantly southwest to northeast. As MSalter says, the wind blowing across the Atlantic picks up water that evaporates from the relatively warm Atlantic Ocean. Then as the rain hits the coast and rises it drops all the water on the first bit of land it reaches - i.e. the North West where I live! Large parts of the south east get only 600-700 mm/year, so it isn't cloudy everywhere in the UK - just the bit where I live.
