The most common and most likely answer to this crossword clue is the 5 plus 3 plus 5 plus 7 letter word SWING LOW SWEET CHARIOT
S
W
I
N
G
L
O
W
S
W
E
E
T
C
H
A
R
I
O
T
More clues leading to the result SWING LOW SWEET CHARIOT
Buddy explains!
The straight part
We know that "Something heard at Twickenham" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case something heard at twickenham = swing low sweet chariot.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.