Britain may be unable to prevent EU fishermen from entering UK waters illegally in the event of a no-deal Brexit because there are not enough vessels to police the seas, an internal government paper has revealed.
The admission could also leave the country more exposed to terrorism, smuggling and conflicts over fish stocks, experts have warned.
It states there is "a lot of uncertainty" about whether the country will be able to police the seas because Britain only has "12 vessels that need to monitor a space three times the size of the surface area of the UK", the document reveals.
It adds: "While our public position on this wider issue is already clear and widely communicated, in that post-Brexit we will be an independent coastal state with control of our waters, both Policy [officials] and MOD [officials] have indicated we are not on an overly strong footing to get ahead of the potential claims that could arise from this story."
The admission has prompted questions about how prepared the UK is to leave the EU without a deal, after Boris Johnson wrote to all civil servants calling on them to making planning for such an eventuality "a top priority".
It has also led to questions about whether the country could face an increased risk of terrorism, people smuggling, illegal immigration and conflict.
Former First Sea Admiral Lord West said: "We do not have enough ships to a protect our fishing zones should we suddenly have a disagreement with the EU about who is fishing where [after we leave] - we just don't have enough ships.
"When you include the job of stopping illegal immigrants, where the navy needs to help because there aren't enough cutters, and smuggling, terrorists and so on, we have not got enough vessels in all the agencies to ensure the safety and security of our territorial seas and the protection of our fishing zones."