well i thought was putting brick in there, instead of the double brick could just go single with the timber :-/ but what do I know, only a dumb sparky I just put wholes in the damn things.
brick veneer (or reverse brick veneer) is no-where as good insulation-wise (and thus, I assume sound proof-wise) as double cavity brick. It's by far the best method, just that it is quite a major job.
As for timber not being as permanent, if you had 2 houses identical in size and shape, one made from double brick and the other full veneer, I give you a crowbar, sledge hammer, saw and a few other demolition tools and see which house takes longer to pull down. My money is on the brick, by a long shot.