It may not be a very hot war - the French still have nukes of their own, after all - but some skirmishes at sea would play very well in some parts of Westminster.

I've already written that, should the Spanish start looking at Gibraltar funny, the Brexiters would start Falkland 2.0 immediately.

Even without a fully 'hot war', there will probably be some semi-officially sanctioned smuggling to "break the new Continental Blockade".