[Transmission]

Does anyone know if it’s still commonplace for the output of live programmes to continue being fed to broadcasters during ad-breaks?

Yes, absolutely, it couldn't work any other way. Though what they'll do and what they'll put on their output will vary between productions. Some might want to do things like rehearse and run through what's happening after the break while others will just sit on their break bumper ready to go. Occasionally they might use the time to record bits for things like promos or e.g. in a football match the presenter might record a quick top and tail for the highlights show.

More often than not you'll find that if the presenters are just chatting away during the break, it'll be all quite anodyne until the moment it sounds like they're about to say something interesting, when someone will remember to cut their mics just in time.