The most common and most likely answer to this crossword clue is the 3 plus 5 letter word OLD GUARD
I've seen this crossword clue in Independent
O
L
D
G
U
A
R
D
More clues leading to the result OLD GUARD
- Conservative faction left in party raised barrier
- Fogeyish folk who may be reluctant to relinquish duties on train?
- Reactionaries one used to give protection on train?
- Conservatives behind the Times newspaper, not the Scotsman
- Gaul regularly ordered around group’s conservative element
- Dinosaurs go off with adult, after shaking T Rex died
- Reactionaries one used to get on the train
- A drug designed to support retired conservative members of group
- Original group members, past their prime, keep watch
Buddy explains!

The straight part
We know that "Reactionaries" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case reactionaries = old guard.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.