Thanks for all the responses....Archie's citronella collar arrived today but I am going to use it in conjunction with the "quiet" command that I have been working on with him.

To be honest the problem isn't really Archie's barking - its my husband's reaction! He thinks sitting on the sofa and shouting "shut up" loudly will work whereas I actually go to Archie when he barks, tell him "quiet" and treat him when he stops!!! If he gets too bad I put him on a lead and he lies quietly at my feet...........

hmmmmm.........maybe I'm training the wrong animal