In reply to Merlin21:
Decathlon do a Simond jacket that has attracted positive comments on UKC
http://www.ukhillwalking.com/forums/t.php?t=570058&v=1
As is often the case, you cannot navigate to it on Decathlon's hopeless website (you can if you're looking for the women's version), but it's here:
www.decathlon.co.uk/alpinism-warm-mens-jacket-id_8271763.html
Otherwise, pick any one of dozens of offerings that has fill weight and features you're looking for... Plenty of threads on 'insulated jackets' or 'belay jackets' if you search UKC.