If your Unifi AP is plugged into the BT router (or whatever)... it will all be the same network. You're good.
It's only if you have an enterprise grade router that every port is a different network (though it is possible to configure them to be a bonded network that appears as a single network).
Unless you're going the whole hog on Unifi... you do not have to worry about this.
I'm thinking of switching to zen internet and they can supply a modem only router, which means I can use ubiquiti router and ap to create long term networking solution, as discussed above only issue is whether I need the switcher for one network to rule them all?
If your Unifi AP is plugged into the BT router (or whatever)... it will all be the same network. You're good.
It's only if you have an enterprise grade router that every port is a different network (though it is possible to configure them to be a bonded network that appears as a single network).
Unless you're going the whole hog on Unifi... you do not have to worry about this.