The Government must clarify when it is legal for British-flagged ships to shoot and kill Somali pirates in the Indian Ocean, a group of influential MPs has said.
The Foreign Affairs Select Committee welcomed moves by the Government last year to allow armed private guards on British vessels sailing off the Somali coast.
But a report published on Thursday said guidance on the use of "lethal force" is very limited, leaving ship captains in a difficult position.
The committee of MPs also concluded that the solutions to combating Somali pirates lie on land, with a need for better support for Somalian civil society organisations and local projects.
And in response to criticism from former captives Paul and Rachel Chandler about the Foreign Office's support for their family during their 13-month captivity, the committee said the Government should review its communication and other procedures when Britons are kidnapped abroad.
Committee chairman Richard Ottaway said: "It is unacceptable that 2.6 million square miles of the Indian Ocean has become a no-go area for small vessels, and a dangerous one for commercial shipping. There is a clear need to take decisive action.
"Naval forces have had some success, but they cannot hope to police such a large area of operation. Ship owners must take responsibility for their own protection, and the Government must let them do so.
"The Government was right to permit private armed guards to defend British flagged shipping against Somali pirates, but its guidance on the legal use of force lacks critical detail.
"The question anyone would ask is that if a private armed guard on board a UK flagged vessel sees an armed skiff approaching at high speed, can the guard open fire? The Government must provide clearer direction on what is permissible and what is not."
Bob Crow, general secretary of maritime union RMT, said: "It is essential that all practical measures are taken to protect UK-flagged ships from the threat of piracy. It is also important that we support those working to deal with the root causes of the continued piracy problem in specific areas around the globe."