The Monarchs of Principalities were considered lesser, so they generally did not take the title, opting for either His Highness or His Serene Highness. On a similar note almost all rulers of princely states in the British Empire were denied the Majesty style, only being recognised as His Highness, a style commonly used for sons (and other relatives) of a Majesty, since they were not sovereigns in their own right.
In the United Kingdom, several derivatives of Majesty have been or are used, either to distinguish the British sovereign from continental kings and queens or as further exalted forms of address for the monarch in official documents or the most formal situations.
Most Gracious Majesty is only used in the most formal of occasions. Around 1519 King Henry VIII decided Majesty should become the style of the sovereign of England. "Majesty", however, was not used exclusively; it arbitrarily alternated with both "Highness" and "Grace", even in official documents. For example, one legal judgement issued by Henry VIII uses all three indiscriminately; Article 15 begins with "the Kinges Highness hath ordered," Article 16 with "the Kinges Majestie" and Article 17 with "the Kinges Grace."
In pre-Union Scotland Sovereigns were only addressed as Your Grace. During the reign of James I & VI, Majesty became the official style, to the exclusion of others. In full, the Sovereign is still referred to as "His (or Her) Most Gracious Majesty", actually a merger of both the Scottish Grace and the English Majesty.
Britannic Majesty is the style used for the monarch and the crown in diplomacy, the law of nations, and international relations. For example, in the Mandate for Palestine of the League of Nations, it was His Britannic Majesty who was designated as the Mandatory for Palestine. Britannic Majesty is famously used in all British Passports, where the following sentence is used:
Her Britannic Majesty's Secretary of State Requests and requires in the Name of Her Majesty all those whom it may concern to allow the bearer to pass freely without let or hindrance, and to afford the bearer such assistance and protection as may be necessary.
Most Excellent Majesty is mainly used in Acts of Parliament, where the phrase "The King's (or Queen's) Most Excellent Majesty" is used in the enacting clause. The standard is as follows:
BE IT ENACTED by the Queen's [King's] most Excellent Majesty, by and with the advice and consent of the Lords Spiritual and Temporal, and Commons, in this present Parliament assembled, and by the authority of the same, as follows: