Fee, fi, fo, fum: f is one of the most English of letters. It was, in fact, the first letter of the ancient runic alphabet of the Anglo-Saxons, the futhorc (named after its opening salvo of letters: f, u, th, o, r, k).
Among familiar four-letter f-words with Old English roots are folk, fair and food. F has also gained spurious associations with Olde English orthography, because a fimiliar f-shape was ufed in former timef to stand for s.
In spelling terms, f presents few problems, apart from a small phonetic variation in the word of (where it represents a v sound). The major spelling complication is caused by the alternative ph (usually found in words of Ancient Greek or Irish origin) which has resulted in innumerable jolly in-service course titles like "Phonics can be Phun".
In one-syllable English words final f is doubled (eg cliff and cuff), although in words borrowed from other languages it might not be (eg clef and chef). Interestingly, there are also a few surnames like ffolkes where the double f comes at the beginning. These originated in a misreading of the Old English capital f, which looked like two small f's intertwined. Spelling mistakes apart, however, the first letter of our forefathers' futhorc does feature in a few important initial double acts: first and foremost, friend and foe, fire and flood, fear and favour, fact and fancy . . .
Fair is foul and foul is fair - formed as it was far back in our folklore, f's definitely a letter to conjure with.