I enabled broadcasting because it was an annoying option getting in my way on the in-game Steam menu, although once I enabled it I realised I did not know how to disable it. Am I being stupid or is it difficult to disable?
In the client, go in the Settings panel, Broadcast's tab.
Here's the support page for broadcasting on steam :
The first time a friend requests to watch your game you'll be presented with the broadcast privacy settings. To make a change at any time, access the Steam Client's Settings panel and select the Broadcast tab to view your privacy settings.
Broadcast is disabled Friends can request to watch my games (default) Friends can watch my games Anyone can watch my games (public broadcast, can be found in the game hub)
However, what isn't mentioned, is that when you restart you PC (and steam restarts) the broadcasting is enabled.
There doesn't seem any way to PERMANENTLY disable broadcasting.