The idea is that the order of precedence prescribes "the order in which men and women arrive, leave, march, are seated, announced or greeted in official functions, ceremonies, receptions, dinners, documents. Certain categories of people are assigned precedence, either by reason of their person (who they are: members of the royal family, peers, knights) or what office they hold (officers of state, judges). Most people are not ranked in any way." (Heraldica). All this is of less importance in the past century or so, but in the 19th century and earlier the rank people held was much more important. A Victorian etiquette book advises the holder of a dinner party to consult Burke's Peerage or an equivalent to see the order her guests should enter the dining room.

Rudra says "I'm under the impression the British Order of Precedence has changed in the past 200 years. I was looking at an old copy of Debrett's from 1864, which placed the Queen's daughters above the Queen's daughters-in law (except for the Princess of Wales). But the 1990 Debrett's places the Duchess of York {wife of the Queen's second son/third child} above Princess Anne {the Queen's second child/only daughter}." The sources I'm using are largely going by the older versions.

Simple Version: Noble Titles This is the bit that causes the most difficulty for Americans -- remembering the order of titles. This is the order, and out of two people of the same rank, who goes first is determined by how long their particular title has been in existence.

However, when you put in family members, things get awkward, because oldest sons (who will inherit the title if it's hereditary) are ranked differently than their younger brothers, and women have their own hierarchy. This is because women can derive rank from their husbands or their own selves. (Husbands cannot derive any rank from their wives.)
Men                       Women
  dukes by creation         duchesses
  marquesses by creation    marchionesses
  dukes' eldest sons        wives of dukes' eldest sons
                            daughters of dukes
  earls by creation         countesses
  eldest sons of marquesses wives of marquesses' eldest sons
                            daughters of marquesses
  dukes' younger sons       wives of dukes' younger sons
  viscounts by creation     viscountesses
  earls' eldest sons        wives of earls' eldest sons
                            daughters of earls
  barons by creation        baronesses
  marquesses' younger sons  wives of marquesses' youngersons
  viscounts' eldest sons    wives of viscounts' eldest sons
                            daughters of viscounts
  earls' younger sons       wives of earls' younger sons
                            daughters of barons
  knights banneret          wives of knights banneret
  viscounts' younger sons   wives of viscounts' younger sons
  barons' younger sons
  knights bachelor          wives of knights bachelor

Close members of the royal family have precedence above their actual titles, so immediately after the ruler come their consort, "2) the heir presumptive, 3) younger sons of the sovereign, 4) grandsons of the sovereign, 4) brothers of the sovereign, 5) uncles of the sovereign, 6) nephews of the sovereign," and all the equivalent women. (Tripod) And then you add in religious or political positions which have been given rank over the centuries, (including some categories which are empty right now, like "uncles of the Sovereign"), and get this list (equivalent female ranks assumed):

  • Her Majesty Queen Elizabeth II (Sovereign)
  • Regent (if there were one)
  • The Prince Philip, Duke of Edinburgh (Consort)
  • Charles, The Prince of Wales (Heir Apparent, because he's male; a sovereign's daughter or sibling, who could be displaced by a sovereign's son being born, would be the heir presumptive)
  • The Sovereign's sons
  • The Sovereign's grandsons
  • The Sovereign's brothers
  • The Sovereign's uncles
  • The Sovereign's nephews
  • The Sovereign's cousins
  • Vicegerent in Spirituals
  • Archbishop of Canterbury
  • Lord High Chancellor
  • Archbishop of York
  • The Prime Minister
  • Lord High Treasurer
  • Lord President of the Council
  • Speaker of the House of Commons
  • Lord Privy Seal
  • High Commissioners of Commonwealth Countries & Ambassadors of Foreign States
  • The following five State Officers if Dukes:
    1) Lord Great Chamberlain (on duty)
    2) Earl Marshal
    3) Lord Steward
    4) Lord Chamberlain
    5) The Master of the Horse
  • Dukes according to their Patents of Creation:
    1) Of England
    2) Of Scotland
    3) Of Great Britain
    4) Of Ireland
    5) those created since the Union
  • Ministers & Envoys
  • Eldest sons of Dukes of Blood Royal
  • The five above State Officers if Marquesses
  • Marquesses, in the same order as Dukes
  • Dukes' Eldest Sons
  • The five above State Officers if Earls
  • Earls, in the same order as Dukes
  • Younger sons of Dukes of Blood Royal
  • Marquesses' eldest Sons
  • Dukes' younger Sons
  • The five above State Officers if Viscounts
  • Viscounts in the same order as Dukes
  • Earls' eldest sons
  • Marquesses' younger sons
  • Bishops of London, Durham & Winchester
  • All other English Diocesan Bishops, according to their seniority of Consecration
  • Suffragan Bishops, according to their seniority of Consecration, and retired Bishops
  • The five above State Officers if Barons
  • Secretaries of State, if of the same degree of a Baron
  • Barons, in same order as Dukes
  • Comissioners of the Great Seal
  • Treasurer of H. M.'s Household
  • Comptroller of H. M.'s Household
  • Vice-Chamberlain of H. M.'s Household
  • Secretaries of State under the degree of Baron
  • High Commissioners
  • Viscounts' eldest Sons
  • Earls' younger Sons
  • Barons' eldest Sons
  • Knights of the Garter if Commoners
  • Privy Counsellors if of no higher rank
  • Chancellor of the Exchequer
  • Chancellor of the Duchy of Lancaster
  • Lord Chief Justice of England
  • Master of the Rolls
  • President of the Family Division
  • Vice-Chancellor
  • The Lords Justice of Appeal
  • Judges of the High Court
  • Viscounts' younger Sons
  • Barons' younger Sons
  • Sons of Life Peers
  • Baronets of either Kingdom, according to date of Patents
  • Knights of Thistle & St. Patrick if Commoners
  • Knights Grand Cross of the Bath
  • Members of the Order of Merit
  • Knights Grand Commanders of the Star of India
  • Knights Grand Cross of St. Michael & St. George
  • Knights Grand Commanders of the Indian Empire
  • Knights Grand Cross of the Royal Victorian Order
  • Knights Grand Cross of the British Empire
  • Companions of Honour
  • Knights Commanders of the above Orders
  • Knights Bachelors
  • Vice-Chancellor of the County Palatine of Lancaster
  • Official Referees of The Supreme Court
  • Circuit judges and judges of the Mayors' and City of London Courts
  • Companions of the Bath
  • Companions of the Star of India
  • Companions of St. Michael & St. George
  • Companions of the Indian Empire
  • Commanders of the above Orders
  • Companions of the Distinguished Service Order
  • Lieutenants of the Royal Victorian Order
  • Officers of the British Empire
  • Companions & Commanders e.g. C.B.; C.S.I.; D.S.O.; O.B.E.
  • Eldest Sons of younger Sons of Peers
  • Baronets' eldest Sons
  • Eldest Sons of Knights in the same order as their Fathers
  • M.V.O. (5th) ; M.B.E.
  • Younger Sons of younger Sons of Peers
  • Baronets' younger Sons
  • Younger Sons of Knights in the same order as their Fathers
  • Naval, Military, Air, and other Esquires by Office.

Sources:
Daniel Pool, What Jane Austen Ate and Charles Dickens Knew, 1993.
http://www.heraldica.org/topics/britain/order_precedence.htm
http://members.tripod.com/historicalnovelists/peeraget.htm
http://freespace.virgin.net/guy.etchells/prec.htm

Note that in precedence Prince Philip does not rank next to The Queen in virtue of being her consort, but because she specifically gave him that rank. Although the wife of a king automatically becomes Queen and ranks first among women, the husband of a Queen has no official precedence as such, unless she or Parliament grant it to him.

Queen Victoria's husband, HRH Prince Albert of Saxe-Coburg-Gotha, was ultimately granted rank next to his wife, much to the annoyance of Victoria's uncles, who were then pushed down one notch. Queen Anne's husband, HRH Prince George of Denmark, was never given any special status and ranked after all other members of the royal family, immediately before the Archbishop of Canterbury. Queen Mary II's husband, William of Orange, was in line for the throne of England anyway and they reigned as joint sovereigns, although Mary's claim to the throne was superior to his. Elizabeth I, of course, never married, and her half-sister, (Bloody) Mary I, married Philip, who was also king of Spain, and was strangely granted the title of King of England as well.

Of course, some countries, like France, got around the issue of what to do with a Queen Regnant's consort by disallowing female sovereigns to begin with.

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