The most common and most likely answer to this crossword clue is the 5 letter word GRUFF
I've seen this crossword clue in Independent
G
R
U
F
F
Buddy explains!
The straight part
We know that "Surly Republican spreads nonsense (5)/Surly" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case surly republican spreads nonsense (5)/surly = gruff.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 GRUFF mean?
GRUFF verb- To speak gruffly.
- Having a rough, surly, and harsh demeanor and nature.
- Hoarse-voiced.