Isn’t it illegal to release them? That’s the case with squirrels
It is indeed illegal to release squirrels but not technically illegal to release trapped mice and rats. However, if the release of the rodent into a different area could be seen to be having an impact on its welfare (i.e. to an area where there is no food, a recognisably harsh environment etc) then it could be seen as inhumane.
Far better to shoot captured rats or whack ’em with something lethal (my favoured tool is a mallet). Besides, as said above, they will more than likely find their way back home if not released far enough away.
What you really need is one of these:
I’m trying to justify the cost of buying one at the moment…