0.1Mohms could be the sign of things plugged in IMHO
Could you do a circuit by circuit IR to narrow down the issues?
I would mention the word rewire to them face to face and see how they react
Get a spark to add a meter in the supply cable to the outside office.
Faffing around with variable rates is pointless
And could you post a photo of the “supply end” breaker for the garden office?
30 - 40 minutes to do an EICR - probably isn't worth the paper its written on
I would ask for a refund
and find a spark to do it properly as this cow boy clearly doesn't know what he's doing
Why did you have the EICR done?
Why a CU in the shed?
What rating of breaker is there protecting the existing cable?
Also fitting a CU falls under part P - who is testing and certifying this ?
Dimplex Quantrum can be wired from a single supply or a dual supply
The downside of the single supply is that the radiators need to be set to heat when the E7 is active