How far British intervention might have gone

If Britain intervened, would the fighting stay in European waters or could an American port face a Copenhagen-style attack?

Probably Europe first. Britain would stop the American fleet there and widen operations in the Caribbean or Canada only if the United States escalated.

The scale of British intervention would depend on Washington's next move. The immediate aim would be to defeat an American fleet sent into European waters, not automatically attack the United States itself. If Washington accepted that defeat, the confrontation might end there. An American escalation against British Caribbean possessions would instead bring stronger Royal Navy forces in the Caribbean and Canada into the conflict.