The most common and most likely answer to this crossword clue is the 5 plus 9 letter word THIRD PROGRAMME
I've seen this crossword clue in The Times
T
H
I
R
D
P
R
O
G
R
A
M
M
E
Buddy explains!
The straight part
We know that "Old broadcaster’" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case old broadcaster’ = third programme.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.