One other interesting date in piecing together the "slippery slope" to war:
15 April 1803 - a month prior to the British embargo - Mortier is placed at the head of an army of 12,000 assembling around Nimègue. I believe this was intended as a show of force: if you don't leave Malta, we'll take Hanover, in effect. Not sure if this was influential in the British actions in May, but it would be surprising if it weren't.
Then we have the Ten Days in May:
16 May - Embargo declared
18 May - British seizure of l'Affronteur by the frigate Doris (what was the excuse given for the seizure?)
20 May - Bonaparte annouces break of the peace by England (presumably due to the seizure, embargo not being an act of war - at least the US used embargo without waging war on Britain)
22 May - Bonaparte orders arrest of all English in France
23 May - Bonaparte orders Mortier to start invasion of Hanover
26 May - Mortier advances into Hanover with 12,000 men
It's interesting that the French didn't declare war either, the announcement being a declaration that the other side had broken the peace - presumably then restoring the state of war that had previously existed. Is there a similar "Bonaparte broke the peace" declaration on the British side, I wonder? Napoleon plainly viewed the seizure of l'Affronteur and refusal to withdraw from Malta as acts of war and certainly the arrest of British citizens and invasion of Hanover were acts of war. Did the British view the seizure of l'Affronteur as an act of war or was there some excuse offered? It wouldn't surprise me if the British viewed the seizure as an innocent act and considered the war thrust upon them by the subsequent actions of Bonaparte (at least publicly).