It could be the quality of your earth grounding. When you say you've had your home electricals checked that would I assume be for the operation of appliances inside the home. The car is sitting outside of the home and the earth potential can be different to that inside the house. When I had my Podpoint fitted the installer found there was a significant voltage difference between my house "earth" potential and the power supply "earth" and both were different from my earth rod. I believe he bonded them and I've never had an issue.
I once had a Renault Zoë on 5 day loan when at my previous house and I could never get the Granny charger to pass it's self-test and that was because early model Zoë was notoriously sensitive to to earth conditions. So much so that I don't believe Reno wood supply why a granny charger with the car from new, it was an accessory.
You may have already done this but I would try why going to friends and family and plugging the car into see if it's over sensitivity of the car car bar-or a problem with your earth conditions at home. Then if you've not had add it specifically.
