He need not worry, the rats will still follow him home. I have a vast amount of wildlife in my garden and most are fine, just three get dealt with. Rats, squirrels and signal crayfish - all with good reason.
How many rats does it take to screw in a light bulb? Two ! but you have to wonder how they got into the light bulb.
Based on that, perhaps we should just cull all the disease carrying humans! We'd have quite a spree right now.
It is illegal to release rats onto any area of land without the owners permission, and as every inch of land is owned by somebody you can't do it, unless you manage to find anyone insane enough to welcome the introduction of dangerous vermin on to their property. Furthermore it is entirely illegal to release into the wild any non native species, and the Brown Rat while common in the UK is not classed as native but is an invasive species.