Britain was vexed by what appeared to be French abrogations of the Treaty of Amiens so declared war on 18 May 1803. Bonaparte immediately resumed planning for a military invasion of England and placed his Grand Army at Boulogne. He collected 20 ships at Brest and Antwerp and persuaded Spain to declare war on Britain. The invasion threat would continue until 1805, when Napoleon decided to move his army to Germany. All hope of naval supremacy in the English Channel was to be denied to Napoleon by Nelson's victory at Trafalgar in October 1805.
Editors. "Britain declares war on France". The Literary Encyclopedia. First published 12 December 2007
[http://www.litencyc.com/php/stopics.php?rec=true&UID=4352, accessed 27 January 2015.]