Donald Trump has indicated that New York Jets owner Woody Johnson will be America’s next ambassador to the United Kingdom. According to the BBC, the President-Elect introduced Johnson as “the ambassador Woody Johnson, going to St. James” at a luncheon. But why is he said to be ‘going to St. James’?
‘St. James’ refers to St. James’s Palace, which was originally built by Henry VIII between 1531 and 1536. At the time, the Palace of Whitehall was the King’s principal residence, and Henry was looking for a retreat from the formality of court life. St. James’s Palace was used as an alternative residence until the end of the seventeenth century.
Following the destruction of the Palace of Whitehall in 1691, the court moved to St. James’s Palace. It remained the Sovereign’s principal residence and the monarchy’s administrative hub until the reign of George III. He found the Tudor building antiquated and uncomfortable, so in 1761 he purchased a nearby mansion known as Buckingham House for his wife’s use. ‘The Queen’s House’ became the royal family’s preferred home, though St. James’s was still the official site of the court and the venue for state ceremonial.
The distinction between the home of the court and the home of the monarch was formalized at the beginning of Victoria’s reign. Since 1837, ‘Buckingham Palace’ has been the Sovereign’s primary residence, and it has become the setting for most ceremonial events as well. However, St. James’s Palace remains the official home of the court and a working royal palace. Today, it houses the offices of the Chapel Royal, the Central Chancery of the Orders of Knighthood, the Royal Collection Trust, and the Marshal of the Diplomatic Corps. It is also the nominal place of issue for many royal warrants, though in reality, they are signed wherever the Queen happens to be.
Ambassadors continue to be accredited to St. James’s because they are technically a liaison between their own head of state and the Queen. However, diplomatic ceremonial is conducted at Buckingham Palace, so Woody Johnson may never actually set foot in St. James’s Palace.
 There some exceptions to this rule. St. James’s is where the Privy Council meets upon the accession of a new sovereign.And because it houses the Chapel Royal, the royal family continue to use St. James’s for certain religious ceremonies. Each Epiphany, a pair of Gentlemen Ushers make offerings of gold, frankincense, and myrrh on behalf of the Queen. The Chapel Royal was also the venue for Victoria’s wedding to Prince Albert and Prince George’s christening.
 Oddly enough, some documents are said to come from Buckingham Palace rather than St. James’s Palace. If there is an official explanation for this discrepancy, I’m not aware of it. However, I’ve noticed that procedural warrants (e.g., warrants directing the Lord Chancellor to seal a document with the Great Seal) refer to St. James’s, while substantive warrants (e.g., the warrant appointing the First Minister of Scotland) refer to Buckingham Palace.
 Nations in the Commonwealth send ‘High Commissioners’ rather than ‘ambassadors.’ This is because, at one time, all Commonwealth countries had the British monarch as their head of state, so the normal rules of diplomatic accreditation would not apply. The workaround was to exchange representatives at the government level, and this tradition continues, even in the case of Commonwealth countries that have become republics.