If 'Earth' was strapped to Neutral, say, just before the domestic meter, would a Neutral short to Earth still trip the RCCB? i.e. like Mig15's system.
Yes - that would cause the RCCB to trip. The way the RCCB works is to compare the current flowing in both the live and neutral wires (remember: mains is AC, or alternating current, so it flows in both directions, in both wires). When the circuit is working correctly current should ONLY flow in the live and neutral wires and be exactly in-balance. Any current flow outside of those wires will cause the RCCB to trip, since the current flow will no longer be equal, which is exactly the point of the RCCB! A short between the Earth and Neutral will allow the current to flow in both Earth and Neutral lines (split as a function of resistance), and will pop the RCCB. The RCCB has no idea where that current has gone, but it will see the imbalance - for all the RCCB 'knows' that missing current could be flowing through YOU!
Typically the trip current imbalance will be 5mA, so any mismatch greater than this will pop the breaker. For humans as little as 50mA @ 120V can be fatal, depending exactly where the current path flows. The worst possible path is across the chest for obvious reasons, so grabbing the live and neutral lines with left and right hands is a VERY bad idea. Many electricians I know will purposefully slip their left hand into their back pocket or belt strap to ensure they don't complete a chest path if they are forced to work on a live circuit.... not something recommended ever but occasionally unavoidable.
- GY