If Britain's only concern is the US, then yes, they can absolutely destroy the American state. A plan for this was made if I am not mistaken, but rejected due to ethical and political concerns. Just take your big fleet, sail it down the coast and annihilate every American city you come across. From Boston to New Orleans, blow them all to smitherines. Harry every coastal village, every hamlet in sight of shore. Just go full Ghengis Khan on the Americans, killing their people, destroying their cities, torching their fields. I don't see the United States being able to bear this rate of attrition for long and they'd probably have to capitulate after a few years.
Of course, why you would want to do this is beyond me. You essentially destroy the land you intend to conquer, undoing generations of effort largely on part of your own government to bend this land into a European mold. Ruling over a pile of ashes is stylish, but not profitable. And of course, the OTL British had better things to do than commit genocide half a world away at this point - like retaking Europe from Napoleon. Even in a peacetime situation, this would have drawn a lot of resistance from other European players. The French would be outraged at such heinous attrocities, and wouldn't that be a lovely reason for war?
So, yeah, Britain could have absolutely crushed the USA, but not at good value for money and not with the international situation being at it was. Or frankly, the domestic one. The British felt some kinship with their colonies, and would not take kindly to such measures either.