Hi Damien, I've (finally) had a response back from the printers via the people I deal with. To be honest, I'm not quite sure what to make of it...
"We print to the values in the file, if Cary is adding ICC or any other profile I would suggest her not doing this as this will alter how the file is read by the Rip. I can understand if she does this to make her own prints sending to a home printer to compensate for colour but please remove any colour tags and make sure she is happy with the image with any profiles removed."