There is no legislation preventing quick dispatch, quite the opposite in fact, it must be carried out quickly and humanely (Animal Welfare Act 2006).
Reportedly there's been a sizeable increase in rat population since Covid with alegedly a 90% increase in London and other urban areas.
Apart from disease and other damage they, (and mice) have a liking for plastic pipes and the insulation around electrical wires with obvious consequences.
They can enter and travel though spaces as small as a 50p and easily climb up the inside of a cavity wall, they can also climb smooth plastic drainage pipes even into a WC bowl. I saw one example where in an unocupied 1st floor flat they had done exactly that, couldn't get out of the bowl as the seat lid was down so chewed through the plastic outlet adapter. In the space of a week they wreaked havoc.
BTW brown rats originated from central asia in the 1700s carried here on ships so naturalised, not strictly native. But then what is? Including humans.
...........So.......... I'll continue to shoot the little bu**ers through the head whenever the occasion arises, humanely and perfectly legal. I don't much care what others do with them as long as they release on their own property and they don't pass the problem on to someone else.