Thanks for all the suggestions. To take them one by one:
“Which breaker is tripping?” – this is the specific RCD for the charger. When they fitted it, they put in a dedicated trip, fed directly from the meter (not via the main fuse board). This has been checked again by the installers (as has the cabling) and no load or earth faults found.
“Did the installers perform a load test following the installation?” – I don’t know.
“Could someone else charge their vehicle from the charger to test it?” – Unfortunately I don’t know anyone else locally with a suitable vehicle.
“Any other appliances running at the same time?” – Generally, no. We do occasionally run the dishwasher overnight, but the tripping bears no relation to that. It will happily trip even when nothing else is turned on. In any event, the breaker that trips is specific for the charger, there is nothing else on that circuit.
This has been reported back to Motability, Ohme and the installers; I spent half an hour on the phone this morning listening to the technical experts scratching their collective heads! Let’s hope that they come up with a solution quickly!
Out of interest, does anyone know why Motability insisted on changing the charger? The old one (Eezee) was working perfectly well.