For more research Vincent Cronin states that there are letters from English agents in Munich and Stuttgart that are contained in the Liverpool papers. Perhaps that is worth looking into?
The royalist Cadoudal ran a training camp 'for conspirators and guerillas' at Romsey in England and after was was declared against France in May 1803, 'English gold' was used to finance the camp. William Windham was the conduit for the financing. Windham and Artois (Louis XVIII brother and future Charles X) informed the British government of the new plot against the First Consul. The British government then alerted 'its agents abroad' and Cadoudal was given letters of exchange worth one million francs.
It certainly appears that the British government was involved.