I agree with you regarding viewership of Rumpole of the Bailey.Rumpole of the Bailey was most popular in the 70s /80s, so could be someone from late 50s onwards. I loved the TV series with the late Leo MacKern and Patricia Hodge (and I'm not in my 70s.) It could still point to Gerry and I think this is very likely. You are of course correct in saying that slander refers to the spoken word.
But, anyone who is wishing to appear legally savvy, AND, actually making a point about slander, would no way in hell be quoting a 40 year old TV programme as a reference/example, would they? Truly laughable, isn't it?
If they were really serious, their terminology would have been far more based on legal advice they had sought before posting their comments.
Well, that is what I would have done.
AND, again, I totally agree with you too, if the CHMN is taking advice from Gerry - God, help them!