Rapha, nice but a bit pricey?

The best down jackets:

• Below £40: don't bother
  
• £40-£100: Decathlon or Uniqlo - the Uniqlo is more stylish but not as warm, and they are (inexcusably) not transparent on their down sourcing
  
• £100-200: Montbell Superior Down Parka or Cumulus Incredilite
  
• Above £200: Montbell EX Light or Mirage if you're going somewhere really cold.
  
  

Arguably the very best is Borah Gear, incredible weight for warmth, but they're not making jackets for another few months. PHD are now charging too much to make a good competitor to the others, but if you need a jacket for -15º or custom dimensions I'd still go there first.

(Note: synthetic may be more appropriate than down for a given usage. Or fleece. It depends.)