For the benefit of our American Cousins ;

       British Peers (Lords) in order of precedence ;

       1) Duke (as in Duke of Edinburgh); Female, Duchess
      
         2) Marquis ( as in Marquis of Bath ) ; Female, Marchioness

         3) Earl (as in Earl of Wessex) ; Female, Countess.

          4) Viscount (as in Viscount Cowdray ) ;Female,Viscountess
      
          5) Baron ( as in Baron Harkonnen !) ; Female, Baroness

            These are all "Lords & Ladies", if you will.In practice,these terms are more often used semi-informally ; I grew up in the household of Viscount Cowdray, but he was always known just as "Lord Cowdray". Below these are Baronets, minor Provincial Peers,created to rule Ulster,Nova Scotia,etc, who are NOT entitled to be called "Lord", oddly ! Example ; Sir John Smith,Bart. (the abbreviation for "Baronet").Wife, Lady Smith.
      Last we have the Knights ; Sir John Franklin, Kt. ( Abbr for Knight).Wife, Lady Franklin.
    Bob Geldof ,Kt, holds an HONORARY Knighthood, and,being Irish,is NOT entitled to be addressed as "Sir Bob", under ANY circumstances. Sir John Franklin was merely (!!) a Knight, NOT a Lord.
   Hope that clarifies things !
                   The Duke of Earl.