The new strain has no doubt already started at least some community transmission in most (all?) of the countries currently banning flights to the UK, we probably just don't know it yet due to lack of identification. For it to also be in Australia already (transmitting it between the UK and Australia isn't exactly an easy task right now...) would tend to suggest it will be pretty widespread before too long. I guess it's a case of taking whatever action you can to not be accused of being complacent, but I'm far from assuming more nations won't be added to the naughty step before too long. Given the UK Government seems to believe it may have started in Kent, I don't think it's certain it wasn't imported on a ferry from the EU in the first place...