Guidance for civil authorities in need of assistance from the armed forces during a national emergency should be improved, according to a group of MPs.
A report from the Commons defence committee stated that advice currently issued by the Ministry of Defence lacks an adequate system for managing the requirements from other government departments and agencies.
The report, entitled 'The defence contributions to UK national security and resilience', was also critical of the small number of vessels dedicated to maritime security.
And MPs raised concerns about the arrangements for co-ordinating maritime forces.
Parliamentary scrutiny of national security issues remains a "developing area", the report stated.
But co-ordination at the political level "might not be as good as it could be" and only reaches "the top of the in-tray" at times of crisis.
The committee called on the armed forces' contribution to be appropriately "understood, directed and resources".
And the report warned that security of the London Olympic Games will be an "immense challenge".
MPs urged the MoD to advertise and exploit the armed forces' expertise during the planning ahead of the 2012 Games.
"If ever there were an emergency where a government department misunderstood what the military could deliver, there could be serious consequences," said committee chairman James Arbuthnot said.
"It is essential that when a request is made for assistance, it is accompanied by a clear statement of requirement."

Dods Parliamentary Communications Ltd