While many monarchical traditions have been lost or evolved throughout the centuries, there are some that still remain in place today. Ambassadors are still given diplomatic papers by their head of state to be presented to the receiving head of state. These letters play an essential role in the ceremony of diplomatic audiences.
Ambassador-designates to the United Kingdom are given two copies of a letter of credence, written by their head of state to Queen Elizabeth II. This letter of credence specifically states that they are being appointed as the ambassador to the United Kingdom.
In Britain, the ambassador-designate is collected from their Embassy in a State landau; this is a ceremonial carriage often seen for diplomatic events.
They first meet with the receiving minister of foreign affairs and presents one unsealed copy of the letter of credence. They then are received by The Queen, as head of state, and present her with a sealed copy of the letter. Once the head of state has accepted the letter of credence, they are then considered an ambassador.
Although St James’s Palace serves a different role now – the London residence of both The Princess Royal and Princess Alexandra, and otherwise primarily acts as administrative space – ambassadors are still formally presented to The Court of St James’s.
While informally, ambassadors are known as the ambassador to Great Britain or the United Kingdom, they are technically ambassadors to The Court of St James’s.
One exception to this practice is that of high commissioners in the Commonwealth. If two nations share the same head of state – in the case of several Commonwealth nations, Queen Elizabeth II – they do not need to present letters of credence. Instead, the prime minister will write an informal letter to the receiving prime minister. High commissioners serve the same role as ambassadors diplomatically.