Puisaye also negotiated with British Prime Minister William Pitt the Younger in London, requesting Britain's support for a royalist invasion of France.

He planned for the invasion to incite the populations of northwest France into rising up against the Republic, as they were mostly royalists, and open a new front of the French Revolutionary Wars; Puisaye even went so far as to claim that he already had an army of 40,000 men under his command in Brittany.

[citation needed] In his negotiations with Pitt, Puisaye convinced him to support the invasion, which he volunteered to lead, requesting men, money and materiel from the British government.

While Pitt approved of Puisaye's proposal, referring to him as a "clear and sensible man," Secretary of State for War Henry Dundas took a more negative view of the invasion.

However, tensions soon developed when a London-based representative of royalists operating on the Count of Provence's behalf in Paris discredited Puisaye, aiming to have Louis Charles d'Hervilly appointed as leader of the invasion instead.

The two officers were not even operating the same plan - Puisaye wanted to take advantage of the element of surprise and attack immediately to relieve Royalist troops throughout western France, but d'Hervilly thought the Chouans were undisciplined and incapable of holding out in open battle, and so planned to remain at Quiberon, fortifying it for use as a base and for pouring in reinforcements.

The division was not only strategic but political - Puisaye was a former Girondin, favouring the establishment of a constitutional monarchy, whereas d'Hervilly wished for the wholesale reinstatement of the Ancien Régime.

The disembarkation happened without difficulty, since the garrison of Auray had been beaten by the Chouans, who had also taken Carnac, Landévant and Locoal-Mendon, putting the coast in Royalist hands.

The Royalist troops thus linked up with the Chouans as foreseen and the villages were occupied, but none of the combined force's operations was put into action by Joseph de Puisaye quickly enough to disquiet the Republicans.

However, the first column dispersed and the second was ready to attack but was met by chevalier Charles de Margadel with news from the Royalist alliance in Paris of a new landing near Saint-Brieuc and diverted towards the Côtes-d'Armor against Cadoudal's advice.

In the meantime, on 15 July, 2,000 more émigré soldiers, commanded by Charles Eugène Gabriel de Sombreuil landed at Quiberon as reinforcements.

Joseph de Puisaye judged the situation hopeless and ordered his men to re-embark onto the admiral's flagship so as to limit the extent of the Royalist defeat and so, despite his later being accused of deserting to save his own life, 2,500 émigré and Chouan troops were evacuated in British rowing-boats.