So the energy meter I have with it's wireless LCD display has no voltage tap, just the current clamp. So it obviously assumes the voltage waveform.
I realise without a voltage tap I would be left assuming the voltage and current waveforms are exactly the same and thus I would miss account anything with a power factor not equal to 1. That would include inductive loads like washing machines, dryers, fridges, freezers etc. and capacities loads, which other than start up bursts of most things with capacitors would, I assume not be very common in a domestic setting.
I would also have to sample the current waveform, determine it's peaks, and crossing points to put my virtual voltage waveform in phase with it.
Or I could try and source a transformer that outputs 3V pp AC from 240V RMS mains. There are ebay modules as I suggested in my original post. Although any solution would need to be fused to prevent any significant current being able to pass through it, so that in the worst case, of say, a short in the device cannot possibly cause fire.
EDIT: I do have a little dual tap 18V sealed 100mA transformer and I could always tap it and run it through a divider to get 3V pp.