The most common and most likely answer to this crossword clue is the 9 letter word WHITEHALL
I've seen this crossword clue in Financial Times
W
H
I
T
E
H
A
L
L
More clues leading to the result WHITEHALL
- British government? Pure rubbish ultimately to a man!
- Short holiday: what everyone needed in one of the 7
- Comic that costs £140 on board and is pink
- British government, bit sorry? Absolutely
- Civil service barrier restricts success, what?
- European lobby in British government?
- British government a little bit sorry? The lot of them!
- Government in spotless country house
- The British government, with Heath ill, reshuffled
Buddy explains!

The straight part
We know that "one of the 7" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case one of the 7 = whitehall.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.