Most mother tongue English speakers can spot, or more precisely hear an Aussie a mile away. It is our broad twang (which is a mixture of British, American, South African and New Zealand)that gives us away. When it comes to Italians, regardless which language I am speaking, most of them think I am either British or American which is a natural response as these are the biggest English speaking groups of foreigners in this country. I don't mind if they can't tell where I am from, however I am a little worried if 'native' English speakers cannot tell where I am from.
I left Australia in 2002 with a big back pack strapped to my back, and a big broad Aussie accent coming out of my vocal cords. I have proof that I used to sound Australian as back in the days before I left the country I was a radio presenter for a big community station. I still have the tapes and it is so funny to listen to how strong my accent actually was! Well naturally it was strong as I had never left the country and I had no friends who spoke English with a foreign accent.
After backpacking for a few months I moved to London at the end of 2002 with my twin sister and her husband (then boyfriend.) We got jobs and I had to speak to many customers over the phone (in particular from Ireland) who could not understand me! As time went by we began to make lots of British friends and day by day, without realising it at first my accent started to sound a little less like mine, and a little more like theirs. I lived in London for just over 2 years, and when I went back to Australia everyone thought it was hilarious that I sounded British.
Let me point out that I sounded British to the Australians however to the British I still sounded Australian.
I only stayed in Australia for 8 months before moving back to London for 6 months, and then starting my time living over here in Italy. Since making the move back to this side of the world in 2006 I have only spoken English (face to face) with British people (or Italian's but that doesn't count.) Of course I may speak to the odd American, or Australian here or there, however my whole life seems to revolve around British people as I work for a British company. I have no control of my accent and it is SO annoying as I can hear that my accent has changed. I can hear (frustratingly) that I sound British! It is the intonation in my voice and I do not know what to do to get my old intonation back.
To make matter even worse, I had one of my British customers the other day who asked me what part of the UK I was from. So now it not just the Australian's who think I sound British, but the British too.