"The fact that a bunch of pirates in Somalia are managing to hold to ransom the rest of the world and our trading system, I think, is a complete insult, and so the rest of the world needs to come together with much more vigor," Cameron said on a BBC program.
The British broadcaster said 49 of the world's 53 hijackings last year occurred off the coast of Somalia.
As many as 200 vessels under the British merchant navy flag regularly sail close to Somalia.
The Home Office said it hoped to begin accepting shipping company licensing requests within a month, Financial Times reported.
The Times said companies with British-registered ships have had to deal with complicated legal and financial implications of carrying armed guards and firing on suspected attackers.
Cameron called the hijacking and ransoming of ships around the Horn of Africa a "complete stain on our world."
Officials stressed firearms should be used only in "exceptional circumstances" and those licensed to carry armed guards would face "stringent checks" to make sure weapons were being used properly.