It's commonly referred to as anticyclonic gloom.
From
http://www.metcheck.com/V40/UK/HOME/
anticyclonic gloom" for many areas of the UK. It's hard to believe that above your head is only around 200ft of thin cloud, above that, blue skies and sunshine.
The change happens overnight tonight. A cold front which has been hanging around the North-west is about to have two short wave troughs run into the back of it causing it to eventually start moving South-east.
The front will bring rain to many areas during Saturday, however it probably won't reach the far South-east until late Saturday evening.
Behind this, a very active area of developing low pressure. This system will push into the far North-west during Sunday with gales, perhaps severe gales in local areas. This combined with heavy rainfall across North-western parts will provide hazardous conditions for a time.
G