When defamation was mentioned in the first article, I assumed it was just sabre-rattling, but they're obviously taking it a bit further. Can't see it coming to court, though, but you never know.
But, legally, think you'd have to be part of a clearly defined group to be defamed in this way. So if it was just about 'Manchester taxis', say, then it would probably be too broad a group and too ill-defined (particularly given the use of the generic t-word) to justify taking action.
(The problem with a reference to a diffuse group like 'taxi drivers' would be demonstrating who precisely the remark was made about, and also as regards demonstrating any tangible reputational damage.)
It's not entirely clear what was said in Belfast, but obviously 'black cabs' is more of a distinct group than 'taxis' generally. And it may be that the reference was specifically to black cabs involved in tours, which seems to be quite a distinct market in Belfast, but it's not clear
precisely what was said.
(And, of course, if a specific business had been named, or individual people, then the obviously it would be a whole lot easier to argue that it's defamatory.)
Another slightly odd thing about it all is how it came into the public domain. After all, if it hadn't all kicked off, the information would have only been seen be quite a small and distinct group of people, and to that extent any reputation damaged and exposure to danger would have been limited. But once it got into the press etc, then the whole world got to know about it
Which, to a degree, would probably limit the liability of who made the original statement, because they weren't responsible for its now very wide dissemination. Which is again another reason I doubt it will get to court. Maybe a public apology and damages settlement
On the other hand, if the claim was effectively GCHQ sourced, then they might well have some evidence to substantiate the allegation, but maybe the problem is tarring a big but clearly identifiable group with the same brush
