More popular are the two Lee brothers Francis Lightfoot Lee, who signed the Articles of Confederation and Declaration of Independence, and Richard Henry Lee, who was the 4th President under the Articles of Confederation. Lesser known are their younger brothers Arthur and William Lee, both patriot diplomats who were in London in 1776.

Arthur was familiar with England. He had studied medicine there in the early 1760s before returning to Williamsburg and establishing a medical practice. He had gained a taste for politics while in medical school, leading a "revolt" against the proposed curriculum that he and other students were successful in changing. He continued his outspoken ways while in Williamsburg, against the suggestions of his friends, which certainly didn't help his business. Feeling more inspired to the cause of America than the cause of medicine, he abandoned his practice and pursued a law degree instead, returning to England in 1768 and attending school in London. Since the mid 60s when he was still in Europe pursuing medicine he had been writting essays, speaking against things like the Stamp and Townshend Acts and advocating for colonial rights and liberties. In 1770 he was appointed by Massachussetts Colony as an agent to London, along with the longtime colonial agent Benjamin Franklin, keeping a line of communication open as well as eyes (and ears) on the situation there.

In 1773 Franklin would make public the Hutchinson letters between the Governor and Lt Governor of Massachusetts that outlined agressive actions to subdue colonial troublemakers. This would cause civil unrest once the Boston Gazette published them. In January of 1774 Franklin was called before the Privy Council in London where he proposed a replacement to Gov Hutchinson. Before deciding on his petition, one member of the Council, Alexander Wedderburn, proceeded to pontificate for about an hour in a highly insulting speech against American liberty, the agitating colonies, and even Franklin himself. Angry, Franklin then refused to be examined (questioned) by the council about the Hutchinson letters and they subsequently denied his petition (the whole thing being labeled the Hutchinson Affair). The next day Franklin discovered the Council had also stripped his position of Post Master and he went from angry to furious; he would seek true American independence from that day forward. When he returned to America the violence at Lexington had occured and he quickly attended to Congress. His welcome status in England had ended on the last day of January 1775 in the Privy Council Cockpit.

Meanwhile for the Lee brothers, William, who had come primarily as a merchant from the colonies to establish business, became sheriff in London in 1774. Arthur finished law school the same year and after admission into the Bar began to practice law in London. He had meanwhile struck up a pen-pal friendship with New England patriot Sam Adams after Adams had been impressed by some of his earlier writtings. His letters with Adams provided fuel to feed the flames of independence in the colonies. Adams would later write to Richard Henry Lee in 1781 about his brother Arthur;

(T)he historian will in some future time draw forth the proofs of his patriotism, and unpredjudiced and posterity acknowledge that Arthur Lee has borne a great share in defending and establising the liberties of America.

In late 1775 Jay, Franklin, and Dickinson of the Congressional Committee of Secret Correspondence would send a dispatch to Lee of papers to be published in London. He had also been appointed "Secret Agent" and began discussions with Caron de Beaumarchais, the French agent (and famous playwright) who would later establish a merchant front to move money and guns to the patriots.

Lee remained in London and was there in 1776 when the Declaration of Independence was signed. In December of 1776 he would join Dr Franklin and Silas Deane in France and work towards their support for the revolution, finally gaining it in spring of 1778. He had also attempted to gain support from the Prussians and Austrians, along with his brother William, but was not as successful there. In 1776 he officially became US Commissioner to France and in 1777 the first US Commissioner to Spain. He would return to the country he helped start in 1780 and be elected to the VA state house as well as be a congressional representative for Virginia. From 1785-1789 he served on the US Board of the Treasury, but due in part to his disapproval of the new constitution would end public service there. He stayed in the new republic, passing away a few years later in 1792.

William had become Alderman after his time as Sheriff ended. He left London for France in 1777 and was soon appointed as envoy to Berlin, eventually establishing residence in Frankfurt. He returned to the US in the early 1780s and unlike his brother largely refrained from politics. He was going blind and had mostly lost his eyesight. He was politically weary from the Deane-Lee scandal but took an appointment to Sheriff of James City in 1790 anyway. He served two years and retired, passing in 1795.

Somewhere in there I should add about the Deane Affair in which Deane was recalled from France and questioned about his arms dealing and book keeping which led to a larger debate where Arthur and William were pitted against Deane. It became a large debate and even Thomas Paine got involved, writing a very long essay titled [The Affair of Silas Deane] (https://thomaspaine.org/essays/american-revolution/the-affair-of-silas-deane.html) that layed out a cause against Deane. Deane lost the battle and was ousted from American politics, but Arthur would forever be stained from the debate. He was likewise recalled from France and his foreign ministry career would end with Jay replacing his position in Spain.

So to answer, yes, two of the originators of American foreign diplomacy were in London, one as an official "Secret Agent" of the Congress.

A fantastic look at primary sources of Arthur's life abroad as a diplomat is the book written by Richard Henry Lee (great-nephew to Arthur, William and Francis Lightfoot, grandson to Richard Henry), [Life of Arthur Lee, LL. D., joint commissioner of the United States to the court of France, and sole commissioner to the courts of Spain and Prussia, during the Revolutionary War. With his political and literary correspondence and his papers on diplomatic and political subjects, and the affairs of the United States during the same period] (https://babel.hathitrust.org/cgi/pt?id=uc1.$b60577&view=1up&seq=12), viewable courtesy of Univ of California.