Thanks everyone!!
Bijou and Katerina - yes the arm detail surprised me - I hadn't really noticed it on the picture. I suspect you are right about it catching. I'm rather clumsy and also don't really like sleeves that are full at the bottom (in practice, rather than aesthetically - I can just see it getting wet when I wash my hands, for example).
Always great to hear from Bijou on weather too, since we live in the same city.
Sterling I kind of like the look of the arm ties too, and the length is in itself ok for me too.
Kathie, Toban and ebfgen I suspect you are right about fit, though I'm also not sure how a trench should fit. I tried the teal coat with a suit jacket underneath (not pictured) and the belt still had folds in it where the fabric was drawn in. Thoughts?
Kathie - I haven't made up my find about length yet. In terms of how to wear it, I hope to begin in late Autumn here in Australia - in May when it starts raining. I do have warmer coats if needed for colder winter mornings. I would wear it to and from work, and also casually for MOTG activities and church. I hope it would be very versatile and give me many years of service as this is a big expenditure in the context of my budget.
Dana and Jenni would I be satisfied with Navy? Hmmm. I can say that navy is much better than black on me - I had a black trench years ago when I first joined YLF and it wasn't good. I also don't want a pastel trench like the lovely one ebfgen has - it looks great but I don't think I could keep it clean enough. My current winter coats are red and pale pink. So not sure!
I think this feedback has been enough to make me send the teal trench back. BTW the other trench I ordered but didn't photograph was in slate and was ASOS brand - it fitted better. So I think Miss Selfridge brand (the teal trench) runs bigger. While you never know without trying, I suspect I could have sized down.
Last question - in pic 5 I feel that I look a bit waistless. I know this is a bit of a recurring issue with me. Is this a deal breaker?