Expat I probably wouldn;t be wearing a huge jumper under because on way to work where the central heating is on full blast and hoping the coat will provide enough warmth to go over thin jumper or cardi
I am darn sarf too
But have just measured bust and am 37-38" which is def a medium on their chart
My down coat if the most fabulous thing I have ever bought - I have been in seriously cold places in it and still been toasty warm, yet it never seems to get sweaty and horrid. And even better, it squashes down to nothing in a vac bag to pack it into my suitcase when travelling
I have a few pairs of their trousers and they are superbly cut but slightly on the generous side. They're good with returns, though. Just be prepared for the spam onslaught when they have your email address - I am sure I get at least two a week from them.