The best introduction to Popper's thought remains the Fontana Modern Masters volume by Bryan Magee - I did not discover Magee's connection with Market Harborough until a few years ago.
But another secondary text I liked at the time was Return to Reason by Roger James. This sought to apply Popper's thought to local and national government and prove that, for instance, the planning disasters of the 1970s, could be explained by various faulty ways of thinking that Popper had exposed.
Searching on the web this evening I was pleased to discover that the whole of Return to Reason has been posted. I don't know how it will read today, but the concept of 'solutioneering' is extremely relevant to the Coalition's current desire to force internet service providers to retain more data about their customers.
James explains the concept in his introduction:
Jumping to a solution before clearly formulating what the problem is (or indeed if there is one at all) or how success or failure are to be judged. Achievement of the solution then becomes the goal; and, when opposition develops, the problem becomes how to get the solution accepted, while the question of how best to solve the original problem, if there was one, never gets discussed at all. I call this mistake solutioneering.