They can have whatever policy they want. . But it should be made very clear of that policy...big/clear signs at the enterence....info on the website etc.
We have a farm park near us that only allow organised school trips. A few years ago it was open to the public. It's made clear it's for organised school trips and that is fine. ..even though I would love to take my dc to see the lambs it's not possible.
The policy should be clear for all to see without having to go searching through the safeguarding policy.