It's done! I've been wearing it! All that "knit one purl one"… I thought perhaps I was mad to want to knit a whole garment in K1P1… but it does make for a lovely knitted fabric. When I started I was thinking of this as more of a "cardigan" but it's quite substantial and definitely more of a jacket.
What I fell in love with and what made me want to knit this jacket… was the beautiful lace panel at the back. It's funny though because now, as I wear it, I realise the part I liked the best… is the part I can't see!!