Britain could be awash with economic refugees if the eurozone collapses and the EU descends into social and political turmoil, according to a group of MPs and peers.
Reporting on the government's National Security Strategy (NSS), which outlines security threats and how the UK would respond, a joint committee said the "plausible" collapse of the eurozone and the subsequent security threats must be assessed as a "matter of urgency".
It blasted the government for being unprepared.
"We are not convinced that the government gave sufficient attention in the NSS to the potential risks that future international economic instability might pose for UK security," the report said.
"These go beyond the UK being unable to afford to defend itself.
"International economic problems could lead to our allies having to make considerable cuts to their defence spending and to an increase in economic migrants between EU member states, and to domestic social or political unrest."
Margaret Beckett MP, chairwoman of the committee, harshly criticised the government's strategy.
"It is good that the government has published a document setting out its national security strategy, but it could be very much improved," Beckett said.
"A good strategy is realistic, is clear on the big questions and guides choices.
"This one does not."
Security Risks of an Independent Scotland
A National Security Council (NSC) was set up by the government shortly after the coalition government took office in May 2010.
The council has yet to address the potential impact of a potential eurozone collapse or Scottish independence, which the report said raises issues around resource sharing, the UK's nuclear deterrent and where armed forces are based.
"The fact that the potential impact of Scottish independence was not brought to the NSC's attention strengthens our concern that the horizon-scanning carried out on the NSC's behalf is inadequate and that the NSC's oversight of security issues is not sufficiently broad and strategic," the report said.
"We are concerned that the Cabinet Office was unable to provide us, either in public or in confidence, with concrete examples of 'blue skies' discussions by the NSC.
"Coupled with its failure to discuss the national security implications of either the eurozone crisis or the possibility of Scottish independence, it is apparent that there are major problems in the way that the NSC selects topics for discussion."
UK Military Intervention Policy 'Unclear' Over Syria
Britain's government needs to be clearer in the principles it applies when deciding to militarily intervene in countries, such as Libya, according to the report.
The government's Strategic Defence and Security Review details an "adaptable posture" that the NSC takes on this issue, which it bases on guidance from the NSS.
"We welcome the idea of an 'adaptable posture' in principle," the report said.
"But in a world in which it was deemed right in principle to intervene militarily in Libya but not, for instance, in Syria, we would welcome more clarity on how this principle shaped decisions on the mix of capabilities to be maintained.
"We call on the government to elaborate on the thinking linking the NSS, the 'adaptable approach' and the capabilities decided upon."