He did very great service in furthering Pitt's policy of maintaining England's influence on the Continent by the arms of her allies, and held the threads of the diplomacy which ended in the king of Prussia's overthrowing the
Patriot republican party in the
Dutch Republic, which was inclined to France, and re-establishing the
stadtholder,
William V, Prince of Orange, in his dictatorial powers. As envoy, Harris immersed himself in Dutch politics from 1784 on and managed to become the
de facto leader of the
Orangist party. He and his French counterpart,
Charles Olivier de Saint-Georges de Vérac, the French ambassador to the
States General of the Netherlands, fought a secret war with the help of
agents of influence, like the then-
Grand Pensionary of the province of
Zeeland,
Laurens Pieter van de Spiegel, and the confidential agent
Hendrik August van Kinckel, and spies like
Pierre Auguste Brahain Ducange. Harris returned to London in secret at the end of May 1787, where he managed to convince the Cabinet to endorse a policy of
subversion in the Dutch Republic, to be funded by £70,000 from a slush fund, laundered through the king's
Civil list. Harris agents used the money to bribe regiments of the
Dutch States Army in the pay of the Patriot
States of Holland, that had deposed the stadtholder as Captain-General of that Army, to defect. The counter-measures of the States of Holland precipitated a political crisis that prompted the States to ask for French mediation. The arrest of Princess
Wilhelmina, the wife of the stadtholder, on 28 June 1782, gave Prussia and Great Britain an opening to muscle in on this diplomatic mediation, and eventually offered an excuse to
intervene militarily. In recognition of his services he was created
Baron Malmesbury, of Malmesbury in the
County of Wiltshire on 19 September 1788, and permitted by
the King of Prussia to bear the Prussian eagle on his arms, and by
the Prince of Orange to use his motto "
Je maintiendrai". In 1786 he told Pitt that France was "an ambitious and restless rival power, on whose good faith we never can rely, whose friendship never can be deemed sincere, and of whose enmity we have the most to apprehend." He also wrote to
Robert Murray Keith: "...from everything I hear and observe, there is not the least doubt that France is working hard at the formation of a League, the object of which, is the Destruction of England." The historian
Paul Langford has claimed that Harris "proved brilliantly effective as a focus for Orangist and anti-French feeling, and as the agent of Anglo-Prussian cooperation". ==Wilderness (1788–1793)==