I know this will be unpopular on this site, but outdoor cats are the nirm here. Most places wont even let you adopt a cat if you cant let it outside. They have been here for thousands of years aleady so any potential damage to wildlife would have happened long ago. Until recently the RSPB even posted research that argued cats dont have any meaningful impact on wildlife species here and their most commonly preyed on species are actually increasing in population. Cats also just like to roam, a house cats territory is on the order of acres of land and houses in the UK are too small to offer them enough space, and they tend to get depressed and agitated if kept inside a small area.

So while in North America its better to keep them indoors, generally in the UK its better to let them roam.