Like many other people, I’m sorry to hear of the death of Verity Lambert yesterday, the day before the 44th anniversary of Doctor Who and the week before her own 72nd birthday. Not many people start a cult TV series before they turn 28. Her professional record was indeed impressive, but I found myself really charmed by her commentaries on the DVDs of early Doctor Who stories, and by a lovely double-headed interview she did with Russell T Davies in one of last year’s Doctor Who magazines. Her legacy, of course, lives on.
I suspect the most common pronunciation is a short, flat a as in “chat”. Certainly that’s how I would pronounce it.