Napoleon wanted to bring around the French and Spanish navies to use for an invasion of Great Britain, but he was stopped by the British Navy. At the Battle of Trafalgar, the French and Spanish brought 41 ships, including 33 Ships of the Line against 33 total British ships, of which 27 were Ships of the Line. Note, that these were major portions of these nations' navies, so it was clearly difficult to build many ships of the line very quickly.

Regardless, at the end of the battle, the French and Spanish lose 21 ships, while the British lost none. Additionally, the French and Spanish lost at least 14 ships of the line in this battle alone. The British came out of Trafalgar as the supreme naval power in Europe, not to be challenged by Napoleon or any other actor. If you want, you can add the Battle of Cape Ortegal, where the French lost 4 more ships of the line to the British.

The British went so far as to fight other nations taking part in Napoleon's Continental System (notably Denmark-Norway during the Gunboat War) to destroy their navies so that the French couldn't use them in order to attempt to invade Britain.

Now, the French could have tried to rebuild these navies to invade Britain, but Trafalgar took place during the War of the Third Coalition. The Continent itself still wasn't pacified as Prussia, Austria, and Russia still presented legitimate threats to French hegemony. With these threats (and rising unrest in Spain), Napoleon couldn't divert resources to plan an invasion of Britain. The best he could do was blockade Britain.

I'm going to take a slightly different tact with this and point out something that Immanuel Wallerstein emphasizes in volume III of his series on the Modern World-System.

When conflict between Great Britain and France broke out in the 1790s it was only the most recent in a series of wars between both States. Famously, Seven Years War (1756 – 1763) ended with a peace that wrested from France the vast majority of its American colonial empire. While the American Revolutionary War (AKA American War of Independence) (1775-1783) had superficially proven a victory for France, in alliance with Spain and of course the American rebels, it also brought the debts of the French Monarchy to even more unsustainable levels.

Despite early hopes for the young USA to serve as an important market for French goods, the decades that followed independence merely provided a new, re-articulated, and stronger relationship between the US and Great Britain (particularly due to cotton). French manufactures were also unable to beat out British goods in American markets.

When war broke out once more in the years after 1789 this proved key. Great Britain had a large fleet already, true, but the fact that it was able to maintain this fleet and heavily subsidize opposition to France on the continent, despite even Napoleon's (admittedly unenforceable) Continental System was due in no small part to the fact that they had unrestricted access to so many non-European markets. Great Britain was trading with China, territories that today make up India, the US, parts of coastal Africa, and after 1808 even into Latin America (Napoleonic invasions of Portugal, 1807, and Spain, 1808, led to the direct opening of their colonial markets to Great Britain).

Obviously there are many military issues at play here that shouldn't be considered irrelevant just because Britain had the upper hand economically. What I'm trying to get at instead is that the years long struggle against Napoleon (which was only part of the decades long struggle against the French Revolution) was only economically possible because of the fact that GB had already won the previous wars for markets beyond Europe. Without the money for prolonged, intensive military action, or subsidies for mainland kingdoms and principates which opposed France, GB would have been unable to keep the war going even if the capacity of their maritime forces gave them short term victories.

Bibliography:

Immanuel Wallerstein: The Modern World-System III: The Second Era of Great Expansion of the Capitalist World-Economy, 1730s-1840s, University of California Press, 2011.

(Re: British expansion into Latin America during this same period) J. Fred Rippy: Rivalry of the United States and Great Britain over Latin America, Johns Hopkins Press, 1929.

(Re: Britain's cotton-manufacture trade networks in Africa, the Americas, and Asia) Sven Beckert: Empire of Cotton: A Global History, Knopf, 2014.