What, we wonder, does Queen Elizabeth II make of the way her prime minister has begun arguing against British independence? The question struck us as we watched this week an interview Mr. Cameron gave to the BBC, where he offered an early glimpse of his case for staying in the European Union. The referendum is now set for June, and the prime minister is suggesting that independence would offer only “an illusion of sovereignty.”

Where does that leave the Crown? We pose the question not out of affection for the monarchy, though neither do we harbor any ill will toward the House of Windsor. Our sentiments are entirely with the American Revolution, which was animated by conceptions of liberty formulated in England and Scotland. These are the ideas of liberty that stirred us to root from the start for Britain’s success in its campaign to exit the EU.

Which is why Mr. Cameron’s remarks strike us as off key. We would have thought that if there is anywhere that sovereignty becomes an illusion it would be precisely within the European project. Its concept of “ever greater union” is calculated gradually to strangle from its member states any capacity for independent action. In one sphere after another — trade, travel, religious liberty, monetary matters — it has becomes inexorable.

The original instinct, emerging after the savagery of World War II, was noble enough. As was the modest congress, convened at The Hague in 1948. In 1950, France’s foreign minister spoke of a pact on coal as making war between France and Germany “not merely unthinkable but materially impossible.” The European Coal and Steel Community led to the Treaty of Rome, establishing the European Economic Community.

Britain moved for membership in 1961, only to be vetoed by Charles de Gaulle, who, we are reminded by a BBC timeline, argued that Britain lacked for commitment to the idea of European integration. No kidding. The best thing that could have happened is for the doughty Brits to have taken the Gallic hint. By 1973, though, Charles de Gaulle was three years into his grave and Britain finally acceded to EU membership.

It took Margaret Thatcher to illuminate the scale of this error. By 1985, the French socialist Jacques Delors was at the helm in Brussels, talking about a single market to compete with the United States. In 1988, Thatcher gave her speech at Bruges, warning: “We have not successfully rolled back the frontiers of the state in Britain, only to see them re-imposed at a European level with a European super-state exercising a new dominance from Brussels.”

Prime Minister John Major’s signing of the Maastricht Treaty, first pillar of the European Union, precipitated a rebellion in Parliament and barely passed. Thatcher, by then a Baroness, declared in the House of Lords that she could never have signed it. The pileup in Parliament unleashed the sentiments that will now be brought to the referendum in June.

Wouldn’t it be something were the Queen to reject as inadequate the reforms her prime minister bought with all his dickering in Europe? She stands, after all, at the head of a monarchy that has been sovereign for more than a thousand years. For Mr. Cameron to suggest all that is an “illusion” almost smacks of lèse-majesté. That’s not exactly an American concept. But how warmly ironical it would be were America, having had, in 1776, an exit from Britain, could extend to Elizabeth a helping hand.