[Stooky Bill]

Even with an analogue desk, a closed mic fader can’t always be trusted.

I remember at a station I once worked at, an engineer tried to do a quick fix on the live, on-air desk and ended up putting the mic live to the left hand channel even though the fader was closed. The presenter was quite a sweary chap too. Thankfully the issue was spotted before any Ofcom issues arose.

At another station it was also possible to get a line out direct from all studio mics into the racks room, so in theory any ‘closed’ mic could still be patched directly to air.

Doesn't even have to be a microphone used for broadcasting, talkback microphones are just as bad. What you say won't appear on air* but colleagues or contributors could hear something they shouldn't. They can be left latched on very easily. Although with at least one system I know well you can route the talkback panels together and listen to the mic without the key being latched..... not that I've ever done that of course, someone told me about it 

Imagine though talking to a contributor before they go on air and then making a comment about them only to find out your mic is still live. 

* although it has happened, I think a Look East bulletin many years ago did