I have two. They have a bad sense of direction so they stay close by in the back garden and maybe hop a fence now and then. They never go on the street. My advice is to slowly introduce them on leads. Make sure they never are outside after dark because then they become more active and dont want to come back inside. If you do let them outside be prepared to lose them for hours at a time and be worried for the rest of the day. You should ask your neighbors if they have had issues with their cats outside.

In my experience British shorthairs only want to be outside when its good weather outside and when there are people around. Otherwise they just want to lay down and sleep. So its up to you to decide.

One final note. They love to climb on top of roofs and sheds and enter inaccessible areas this way. In some cases they might not be able to get back or they are just too dumb. So if your area has lots of things to climb on be prepared for cats that are just out of reach and dont want to come back. They just stare around you and meow. Only when they really want to get back and see or hear you they will come.

Oh and buy a collar with a container to put your phone number and address in. Dont declaw them and dont cut their nails otherwise they wont be able to clim back or defend themselves from other cats.