The most common and most likely answer to this crossword clue is the 5 letter word ISLES
I've seen this crossword clue in The Daily Telegraph
I
S
L
E
S
More clues leading to the result ISLES
Buddy explains!

The straight part
We know that "British locations, say" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case british locations, say = isles.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 ISLES mean?
ISLES noun- A wing of a building, notably in a church separated from the nave proper by piers.
- A clear path through rows of seating.
- A clear corridor in a supermarket with shelves on both sides containing goods for sale.
- Any path through an otherwise obstructed space.
- Seat in public transport, such as a plane, train or bus, that's beside the aisle.
- An idiomatic divide between the Republican Party and the Democratic Party, who are said to be on two sides of the aisle.
- A (small) island, compare with islet.