The most common and most likely answer to this crossword clue is the 7 letter word MUDLARK
I've seen this crossword clue in The Daily Telegraph
M
U
D
L
A
R
K
Buddy explains!
The straight part
We know that "Urchin" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case urchin = mudlark.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 MUDLARK mean?
MUDLARK noun- A pig; pork.
- One who scavenges in river or harbor mud for items of value, especially in London.
- A child who plays in the mud; a child that spends most of its time in the streets, a street urchin.
- A soldier of the Royal Engineers.
- Any of various birds that are found in muddy places or build their nests with mud, especially Anthus petrosus and Alauda arvensis.
- The Grallina cyanoleuca that builds its nest with mud into a bowl-like shape.
- A racehorse that performs well on muddy or wet tracks.
- To scavenge in river or harbor mud for items of value.