Originally posted by val
If a law does exist, what if we broke it? Would the owner of the found pet be able to sue us in civil court?
Yes, In England, I have read several legal cases that owners have brought against people stealing/picking up their cats. as I mentioned we have a seven day minimum wait before rehoming , the only exception is medical need (i.e. If they are in pain and need to be PTS)

In one case a couple sucessfully got additional money as the shelter who picked up their cat and altered her without permission. (Though I think that is stupid to have a free roaming entire cat)
Originally posted by val
Does the leash law that most counties have trump that? I think any judge in his right mind would believe I did the right thing by getting the animal to safety, but would letting the pet roam be considered neglect?
In England roaming cats are consider healthy and happy not neglected, in fact our cats have the legal right to roam unlike dogs which have a national leash law. (Dangerous Dogs Act)

I can not see any judge objecting to people picking up cats they are concerned about. That is a fine thing to do to help the cat in question, but if little or no effort is made to find the owners before rehoming said cat...legal action may follow.