In any case, Britain will find that, unless it is willing to continue sharing access to its waters, it will lose access to valuable foreign markets.
Consider Norway, which as a non-EU member has control of its own waters.
It nonetheless co-operates with the EU and other countries over fish quotas in 90% of them, in order to maintain its own fishermen's access to fisheries inside the EU.
Of the 700,000 tonnes of fish landed in Britain each year, some 500,000 is exported, two-thirds of it to the EU.
Without a mutual deal, which would surely include giving European fishermen some access to British waters, those exports would face World Trade Organisation tariffs averaging some 12%.
In the past the EU has responded to fishing disputes with Norway and the Faroe islands by banning all imports.
British fishermen would soon find that, to borrow a phrase from the Brexiteers, “we need them more than they need us”.
Consumers would notice, too, since most of the fish on British dinner plates is imported.
A third of it comes from the EU, and British fishermen net about a sixth of their total catch in French, Belgian, Dutch, Danish or Irish waters.
Britons may decide that they are willing to pay higher prices for the privilege of banning foreign vessels from British waters.
But such a rule would have to be enforced, at extra cost.
The “cod wars” with Iceland in the 1950s-70s saw gunboats deployed to protect fisheries.
Some Brexiteers would doubtless enjoy such a muscular exertion of sovereignty.
But for ordinary Britons who, since the referendum, have endured a squeeze on incomes comparable to that during the financial crisis of 2008, the fishing industry is a distraction.
The aviation business is bracing for a hard exit.
The finance industry, which contributes 7% of GDP, is in danger of decamping.
Britain's Brexit negotiators have bigger fish to fry.