Don't buy feathers for use in the UK. wet down sleeping bags are useless
This argument is getting a little long in the tooth, i agree wet down is useless but why would you let your down bag get wet in the first place ?
I have used a down bag for years, including winter camping\climbing trips, down allows high warmth to weight ratios and small pack sizes.
The trick is you keep it dry, the combination of a good tent and a dry bag is all you need to do to achieve this.
Having said that i wouldnt use down in summer, you will really need 2 bags to cover you for all year round, spring and autumn you would want a down bag thats capable of going down to inbetween 0 to -3 and summer a nice light synthetic thats good for +2 upwards.
Depends how cold you get of course but that should cover all bases and you need extra warmth you can use a silk liner which would give you another couple of degrees.
That is all !!