Will bonding cause an MCB to operate?

[ebee]

Even with ideal insulators, in an AC system, a sufficiently large system of interconnected metal is effectively an earth reference, even if there is no conductive path to earth.

Agreed, not just a conductive path (however small) but also an inductive path or a capacitive path might give us some reference to "Earth" or some other potential.

We sometimes refer to "Earth" in the humble motor car but usually the sit on tyres full of air so no real earth about and when some say earth they really mean chasis which is not the same thing.
Some even sometimes add little insulating strips to link chasis to road earth by some bizzare logic but unless there is some conductivity then how can that work?

 

[JohnW2]

Even with ideal insulators, in an AC system, a sufficiently large system of interconnected metal is effectively an earth reference, even if there is no conductive path to earth.

Whilst that is literally true, qualitatively, I doubt whether (m)any domestic premises have "a sufficiently large system of interconnected [and touchable] metal" for what you say to be particularly 'significant'.

In any event, in the context ebee raised the issue, isn't it earth-refencing of the supply (i.e. at the transformer) that primarily matters? ... and, in the absence of a direct (conductor) connection to earth, I can't see why any capacitive or inductive coupling should preferentially be to one of the 'outputs' of the transformer?