In reply to
Charcot Marie tooth:
The brands the you mention are all quality, which will offer options up to the level you'd need for Arctic or Everest expeditions. But as you say the likes of the Rab Microlight is a relatively thin jacket and not really enough for winter use, so really important to look at fill ratings (how much down) and not just the brand.
One thing you will find is that most genuine outdoor brands drop down at the back to cover the kidneys (really helpful if sitting as it prevents a cold spot at the base of your back), more fashion orientated brands tend to sacrifice this for a straight cut at the waist as it looks more stylish.
I'd also second a suggestion from someone to look at synthetic rather than down, as they are far more forgiving to the British climate (getting wet) than down. Slightly heavier and usually don't pack down as small, but that won't be an issue for how you want to use it.