 In the Len Deighton (qv) novels the name of the lead character is  never revealed. So Michael Caine (I) (qv) and producer  Harry Saltzman (qv) tried to think of a boring name for the hero.  Caine suggested "Harry" which Saltzman found rather amusing. Caine  then remembered a boring classmate named Tommy Palmer. So "Palmer"  became the surname.