What were the weapons use by Great Britain in the 1940s?Which of the weapons was most useful?
The advent of city bombing was one mainly driven by Churchill's fascination with the idea of aerial bombing being used to devestate an enemy and cause a quicker end to the war. He and his military advisors were well aware of the fact that their bombs were rarely hitting their targets but he continued to push for larger and larger bomber forces and larger and larger raids all the way through the war. This was a relatively new development, one which was later copied by the Germans as well as the US.
Along the lines of aerial bombing, the British were also heavily involved in the development of incendiary bombs, meant to burn large portions of enemy cities and worked with the US Air Corps to develop the Bouncing Bomb which was used to destroy dams after bouncing over torpedo nets and other obstacles.
I'll assume you mean during World War II. Britain had a number of weapons that it used during that war, including the Blenheim Bomber, the Hurricane, the Spitfire (heroes of the Battle of Britain), the Sten submachine gun, and he Churchill and Challenger tanks.
Hard to argue which was the most effective, as they were used in different ways at different points of the war. I guess I would have to give the title to the Spitfire, which came into production just in time to hold off the German air force during the Battle of Britain. Almost anyone who's ever flown one has written or spoke of how she handled like a "kite".