The most common and most likely answer to this crossword clue is the 7 letter word EXAMPLE
I've seen this crossword clue in The Daily Telegraph
E
X
A
M
P
L
E
More clues leading to the result EXAMPLE
- Instance of former politician overwhelmed by drink
- Formerly large case
- Specimen is old enough
- Former lover, large specimen
- Former partner, big enough for a model
- Old member overwhelmed by drink, for instance
- Former politician dipping into drink for instance
- Model no longer, having got “wide”
- Model partner once generous
- Beer drinking backbencher maybe on English vote: it's a warning
Buddy explains!

The straight part
We know that "Warning" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case warning = example.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 EXAMPLE mean?
EXAMPLE noun- Something that is representative of all such things in a group.
- Something that serves to illustrate or explain a rule.
- Something that serves as a pattern of behaviour to be imitated (a good example) or not to be imitated (a bad example).
- A person punished as a warning to others.
- A parallel or closely similar case, especially when serving as a precedent or model.
- An instance (as a problem to be solved) serving to illustrate the rule or precept or to act as an exercise in the application of the rule.
- To be illustrated or exemplified (by).