Hey warwickwater,
I think I have found a solution. I found a library that a user wrote that will allow a websocket to be set up so that you can push messages to an arduino from a web server. I have just discovered it and am not sure of all the details, but here is the link to the code and info:
I found it through this code/project, which lists other dependencies other than just the arduino library for the system to work. I'm not sure if I need it yet, but I'll link it so you can look it over as well:
Good luck, and I hope this helps!