“So the principal Theme never appears, even as in some later dramas – e.g., Maeterlinck’s ‘L’Intruse’ and ‘Les sept Princesses’ – the chief character is never on the stage.”
Edward Elgar from the 1899 program note for the Enigma Variations
Elgar routinely entertained himself with ciphers and anagrams, so it is remarkable his reference to Maeterlinck in the original program for the Enigma Variations presents some intriguing parallels with the name Martin Luther. First, the letters in the first, second, fourth and seventh letters of each are exact matches (M, A, T, and L). Second, there are three equidistant letter matches (R, I, and N). Finally, when including the possessive s with Maeterlinck as it appears in the program note, the number of letters is identical.
Do these intriguing parallels suggest the presence of something more, a cipher? Elgar was an acknowledged expert in cryptography, so it is not unreasonable to suspect he deliberately inserted the Maeterlinck reference as a subtle link to the covert Principal Theme and its composer. Is there some plausible connection between the Maeterlinck and Martin Luther? The answer is a resounding yes.
One possible anagram of MAETERLINCK is CEEK MARTIN L. Elgar is known to have used c as a substitute for the letter s. For example, he spelled the word score as ckor, skore, skorh, skowre, skourrghe, csquorr, skourghowore, and ssczowoughohr.  In light of this insight, the anagram CEEK MARTIN L may be read as Seek Martin L. By means of such an anagram, Elgar cleverly invites the audience to seek out Martin Luther, a composer whose most renowned musical work is Ein feste Burg.
Another anagram derived from MAETERLINCK is a slight variant of the first – C EE K MARTIN L. Before providing an interpretation, let us review some relevant information. The letter C is the phonetic equivalent of the word see. Edward Elgar routinely signed his letters with the initials EE and used the letter K to indicate that a copy of a score had been made. Based on this information, C EE K MARTIN L may be read as See Edward Elgar copy Martin Luther. This rendering alludes to Elgar's use of Ein feste Burg as the covert Principal Theme to the Enigma Variations, a form of musical borrowing in which he essentially copies Martin Luther's most famous hymn by means of counterpoint.
Some may object that too much is being read into Elgar’s literary reference to Maeterlinck in the 1899 program note for the Enigma Variations. The reality is just the opposite is the case, that too little has been read in Elgar's carefully worded program note beyond the ordinary surface meaning. Elgar reveled in word play, and this example is no exception. The word program rhymes with anagram. The name Maeterlinck sounds like the words meter and link paired together. Meter is a musical term, and the combination with the word link may be viewed as a cryptic hint about some musical link to the covert Principal Theme. Program, anagram, Maeterlinck, meter, link – this is just the sort of wordplay that would fire Elgar's inventive imagination. To understand and appreciate Elgar and his music (particularly the Enigma Variations), it is essential to venture beyond shallow superficiality to perceive a deeper, hidden meaning. To do so is the essence of cryptography, and Elgar. To learn more about the secrets behind one of Elgar’s most celebrated symphonic achievements, read my free eBook Elgar’s Enigmas Exposed.
 Cited from an unpublished paper by Eric Sams entitled Elgar’s Cipher Table (1970-71).