@PigletJohn - eh? I’m Australian. I’ve done this exactly once and would never do it again.
In my early twenties, I moved to a small town for work. Now, in this particular place, people are a lot more casual with social arrangements than they are in the city I’m from. One of my superiors at work invited me to dinner with him and his wife. All went well, both lovely people, and both told me repeatedly that I could drop in anytime. At first I thought this was just a thing they said to be polite, but he kept reiterating it when I saw him at work. He even sort of (gently) admonished me for not dropping by.
So, one Sunday afternoon, I did it. The reception I got was along the lines of “Oh, it’s you, what do you want?” I’m sure the words they used were more polite than that, but that was the gist. I was mortified. On the spot, I made up a work-related excuse to speak to him. We talked about work for a bit, then they offered me a drink and I said “Oh no, must be off”, because they clearly wanted me gone.
So, yeah, I would never advise anyone to show up unannounced, even if you are told you will always be welcome.