IF the attck on the French fleet at Mers-el-Kebir took place July 1940 (I cannot find a reference anywhere ITTL) Then Vichy will have attacked Gibraltar
https://afterburner.com.pl/24-september-1940-french-air-raid-on-gibraltar/
so the UK is already at war with Vichy France.
The British still have the French to worry about so any decent warships will be somthing they want.
The British will also want the American Fenians who have been funding the Fenians in Ireland.
I would imagine that New England would be pushing for a settlement that did not leave them with a...
"An army marches on its stomach" It is December there is little chance of resupply from the continent. The local population will be secreting its food stores, Napoleon has a problem the British should have a much better chance of obtaining supplies.