Vets with commercial experience with chickens wouldn't have much of a clue when dealing with a pet. For a start they often diagnose illness by post-mortem, which isn't particularly helpful on an individual basis. The best domestic chicken vets are on the BHWT list I'm told. We are in a similar problem with vets here because the poultry keepers just kill the sickies, make no apparent attempt at diagnosis and won't spend the money at the vets anyway.
Interesting to know what the symptoms are that lead you to diagnose egg bound or peritonitis HeatherB? Egg bound would be repeated trips to the nest box and a pulsating vent, sometimes the egg can be seen. A wipe inside the vent with vaseline works. Peritonitis will be a penguin stance with distended firm rear abdomen. Green poos would signify infection. One condition is pretty harmless, unless they prolapse or the egg breaks, and the other should be PTS- unless you go down the abdominal drain and hormone implant route (about £200).