The most common and most likely answer to this crossword clue is the 11 letter word READMISSION
I've seen this crossword clue in The Times
R
E
A
D
M
I
S
S
I
O
N
Buddy explains!
The straight part
We know that "allowing visitors back in" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case allowing visitors back in = readmission.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 READMISSION mean?
READMISSION noun- A second or subsequent admission