I am going to recommend a history book as the best way to understand British politics today.
Andrew Marr, <em>The History of Modern Britain</em>
Marr is an excellent storyteller and covers the politics of postwar era to 2007.
By taking a decade-by-decade approach of the hot political topics of the time is it is an excellent cover of the story how we got to where we are today and earlier political struggles that brought them about.
Only 99p for the book. Also got made into BBC TV series, if that format suits you better.