The most common and most likely answer to this crossword clue is the 6 letter word VOWELS
V
O
W
E
L
S
More clues leading to the result VOWELS
- Five characters, wolves in disguise
- Set of letters found in post, ultimately
- Regularly gave wino rum for them
- Five elected initially to enter parliament — I for one, and four others
- Class of sounds, all used in audiometry
- Promise the Spanish Society these letters?
- Very wise birds going around England…London has two of them
Buddy explains!

The straight part
We know that "London has two of them" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case london has two of them = vowels.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.
What does VOWELS mean?
VOWELS noun- A sound produced by the vocal cords with relatively little restriction of the oral cavity, forming the prominent sound of a syllable.
- A letter representing the sound of vowel; in English, the vowels are a, e, i, o, u, and sometimes y.