The most common and most likely answer to this crossword clue is the 1 plus 4 plus 2 plus 1 plus 5 plus 4 letter word A BULL IN A CHINA SHOP
I've seen this crossword clue in The Times
A
B
U
L
L
I
N
A
C
H
I
N
A
S
H
O
P
Buddy explains!

The straight part
We know that "blundering disaster" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case blundering disaster = a bull in a china shop.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.