Holy smokes this dress is beautiful. And so massively versatile - can be worn belted (with fabric belt that comes with it or an alternative leather belt), loose more as a kaftan or can be worn open like a loose duster coat/ kimono.
Vintage Allegra Hicks.
It would be a good fit for a UK8 (slightly oversized) - UK12 (loosely fitted) but I'd say the best fit for a UK10. Sits on the knee in length (based on a height of 5'7").
In excellent vintage condition.