#9 I would have said it was only a speech defect, like a lisp
GB ENS here. I agree with the above; there is no accent that I know of where this is normal.
The speaker in #5's video appears to have a very slight tendency to sh all his s's. Sean Connery was the same, but more obvious.
As for John Campbell, his accent sounds like NW England to me; I wouldn't like to guess more precisely.*
Regarding sibilants: at the start of the first video (via the link in #15), he says "nurse" repeatedly, also "science" and a lot of other words with 's', and pronounces them all clearly.
* Have just noticed that his Twitter handle is "JohnInCarlisle", so perhaps it's there.