I have to profess to know very little about this other than it is caused by a fungus but which one I do not know.

I did a 'google' and found this perhaps reading the articles might enlighten you better.

http://www.ehow.com/about_6367896_fir-tree-fungus.html

Sorry I couldn't be of more assistance...Tg

Which branches are going brown? Are they near the base, or all over? And where in the UK are you?

if there near the base it could be natural loss .

jellybaby here thanks for your commentseveryone about norwegian spruce the brown on arms are on branches all over the tree not just at base never happened befor first year i live in suffolkby the broards a little village northcove

Check the bark from top to bottom (if you can) for signs of invaders, or flaking anywhere, to make sure its not bark beetle infestation. There is a bit of a problem with Great Spruce Bark Beetle, and if its that, you need to tell the Forestry Commission. Fungal infection sometimes occurs with the beetle, but usually it shows as a bluish/blackish deposit on the needles and branches. Also check for orange spores or nodules - if any are present, it's a different fungal attack to which these trees are prone, and there's no treatment other than to remove and dispose of infected needles.