Theresa May is expected to announce within weeks that the UK will reclaim its waters for British fishermen by pulling out of a deal that pre-dates the EU.
The Prime Minister will take Britain out of the 1964 London convention which allows European fishing vessels to access waters six to twelve nautical miles from British shores.
Pulling out of agreement would mean a clean slate for British fisherman after Brexit, although the Government could seek to secure a new deal during the negotiations.
Brexit will spell the end of the hated Common Fisheries Policy and enable the UK to assert control over its 200-mile Exclusive Economic Zone (EEZ).
But Mrs May will also need to serve a notice period of two years to exit the 1964 agreement.
Sources at the Environment Department said that because of the notice period, "there is a logic" to withdrawing at the same time the Government invokes Article 50.
Mrs May has informed the European council that she will trigger Brexit on Wednesday 29 March.
The Telegraph understands that talks have been going on for months with other members of the 1964 deal about Britain's withdrawal from the agreement.
A major report published last October found that more than half the fish caught in British waters are currently landed by trawlers from the rest of the EU.
Alan Hastings, a fifth generation Ayrshire fisherman and a director of Fishing for Leave, said: "The Government must serve notice of pulling out of the 1964 convention at the same time as invoking Article 50.
"The fact that they haven't already announced that is giving us the jitters. So far they have used the right rhetoric but their actions have not lived up to that."
Mr Hastings wants the Government to scrap the quota system of fishing, which leads to huge numbers of fish having to be discarded after they have been landed.
The EU's quota system dictates precisely which species of fish, and how many, fishermen are allowed to catch.
Instead Mr Hastings wants a "days at sea" system, which would allow fishermen to fish freely for a set number of days, but which is constantly monitored to prevent over-fishing.
In countries where the days at sea system is used, fishermen can be ordered to return to port - or to stay in port - at any time if they are deemed to be over-fishing.