Solution to Puzzle 17

Last week I published this puzzle:

R D L T Y D H Q R H W S J A A R L E A O O C L Y U
U Y N J T G R I O X B L D M M V D E O U P L R A Q
E D E O X B I S P B L F T F K P L Y Y V W C Z W A
D R H M N G T N V U U Y D R H M N Z N S E C U W T
C W M J C Z L B L P C O Y D P X P B L Y U U Y N V
D E C R Z C B N D Q Q R D I Y O D E M N H C V Y O
M R I S L Y Y U G R I

If you haven't yet attempted it, you may wish to do so before moving on.

To solve this you would have first tried to establish the key length, and then looked at the frequencies of letters encoded with identical key letters. This would have allowed you to make good guesses for each key letter, and then form the plaintext.

This text was prepared using the Cipherclerk applet, the input text was a quote from the Lenny Henry show, 'Chef!'

L E T M E E X P L A I N T H E O R D E R O F T H I N G S T O
Y O U T H E R E S T H E A R I S T O C R A C Y T H E U P P E
R C L A S S T H E M I D D L E C L A S S W O R K I N G C L A
S S D U M B A N I M A L S W A I T E R S C R E E P I N G T H
I N G S H E A D L I C E P E O P L E W H O E A T P A C K E T
S O U P T H E N Y O U

Reformatting the text we get this:
Let me explain the order of things to you. There's the aristocracy, the upper class, the middle class, working class, dumb animals, waiters, creeping things, head lice, people who eat packet soup, then you

Source: Gareth Blackstock (Lenny Henry), Chef!

Enciphered using 'Beaufort cipher'.
Using the alphabetic key 'chef'.
The length of the plain text is 161 letters.

Plain text alphabet is 26 Letters: A-Z.
Operation Mode:Repetitive Key

Within beaufort, the enciphering and deciphering operations are identical, and so it does not matter which is chosen for decryption.