I suspect that the forces wouldn't allow such a survey to take place because of their desire to be seen as politically neutral.
However, my personal experience of people who have served in/with the armed forces indicates that they're inclined to be rightwing monarchists. I suspect that those serving in the police force would be a similar demographic.
This article discusses the political leaning of the armed forces:
https://bylinetimes.com/2021/10/22/military-matters-91-of-mps-with-armed-forces-background-are-conservatives/