When he finally diagnosed consumption, he put Keats on a starvation diet of an anchovy and a piece of bread a day, to cut the flow of blood to his stomach.

He also made contact with members of the European royal families and aristocracy, among them Prince Leopold, later King of the Belgians, as well as English aristocrats travelling in Europe.

He steadily built up a medical practice in London, and in 1829 published what was described as his "best and most important work",[1] The Influence of Climate in the Prevention and Cure of Chronic Diseases, more particularly of the Chest and Digestive Organs.

In it, he systematised and popularised all that was known about the subject, and gave a more correct view of the powers of climate and mineral waters in the treatment of disease than had hitherto existed in the English language.

He thought it "not beneath his notice or his dignity to study the art of prescribing practically, and by repeated trials, and his prescriptions compared favourably with those of most of his contemporaries.

[1] On 11 November 1837, sixth months after Victoria's accession to the throne, Clark was appointed the Queen's Physician-in-Ordinary, and was created baronet of St George's Hanover Square, London.

Lady Flora's enemies, Baroness Louise Lehzen and the Marchioness of Tavistock then spread the rumour that she was pregnant, and the Queen wrote in her journal that she suspected that John Conroy, a man she loathed intensely, was the father.

It was assumed by the public at the time that Clark had "given support to a slander against [Lady Flora]'s character by sharing suspicions which his medical knowledge should have dissipated.

Conroy and her brother, Lord Hastings, stirred up a press campaign against both the Queen and Clark which attacked them for insulting and disgracing Lady Flora with false rumours, and for plotting against her and her family.

Always about the Court, high in the favour of the sovereign, and known to be greatly esteemed by the prince consort, he became the person to whom statesmen constantly referred for advice connected with medical matters and polity.