The report, known as Operation Yellowhammer, said: “Up to 282 EU and European Economic Area nations’ fishing vessels could enter illegally or are already fishing in UK waters.
“This is likely to cause anger and frustration in the UK catching sector, which could lead to clashes between fishing vessels and an increase in non-compliance in the domestic fleet.
French fishermen have already warned they would stop British fish being sold in France if they were barred from the waters.
Regional fishing committee’s in Northern France have even threatened to block Calais.
Chairman Oliver Lepretre said: “If there is a hard Brexit, I can assure you that not a single kilo of seafood or fish from Britain will get into France.
Current EU laws make 12 nautical miles around the coast of Britain free to use for foreign ships.
International boats are also given access to up to 70 percent of the quotas for ground stocks in Britain.
France alone lands 120,000 tonnes of fish from the UK fishing zone, with the Netherlands and Denmark netting 177,000 tonnes and 237,000 tonnes respectively.
Polls claimed 92 percent of those in the industry voted to leave the European bloc, with concerns on the CFP at the forefront of the debate.
Fishermen say leaving the EU would see the sector boom without stringent CFP rules on the amount and type of each fish that are allowed to be caught.
Fishing for Leave said: “On taking office as Prime Minister, Boris Johnson said he would energise the United Kingdom.
“One way of doing this which would be both hugely beneficial and environmentally rewarding is for the UK – abiding by International law – again to manage our nation’s Exclusive Economic Zone (EEZ) of 200 nautical miles/median line zone and doing so in a far superior way to the Common Fisheries Policy.
“This would benefit the living marine resource and our coastal communities and if we moved away from quotas to an effort-based system, it would place the UK as a world leader in this field.”
The group has previously warned the government must take a zero-tolerance approach to illegal fishing, adding impoundments and fines should be imposed for those that break the rules.
But 13 percent of the UK’s fish stock comes from countries in the European Union, something Britain would lose on a no deal exit.
A total of 65,000 tonnes of fish are caught in Irish waters, with 14,000 tonnes coming from France.