Got there in the end
If you wanted to use a snippet to get the id it would need to be called cached within an un-cached WebloginPE call like :
[!WebLoginPE? &type=`users` &usersList=`All Users:default:default:username:ASC:internalKey([[AuthorID]])` &usersTpl=`designerListTpl` &viewProfileTpl=`viewProfileTpl`!]
Just for the benefit of other readers.
