The most common and most likely answer to this crossword clue is the 4 plus 7 letter word FIRE BRIGADE
I've seen this crossword clue in The Daily Telegraph
F
I
R
E
B
R
I
G
A
D
E
More clues leading to the result FIRE BRIGADE
Buddy explains!
The straight part
We know that "that lot can go to blazes" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case that lot can go to blazes = fire brigade.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.