My house (I live in the UK) failed an electrical safety inspection because of a missing main supply cover. I have tried using google to find one to buy but can't find anything at all. Does anyone know how I can go about getting the right kind of cover for this?

For context, the unit is connected to the electricity meter

UPDATE: I reported this to UK Power Networks after the advice I got here and they booked somebody to come out 2 days from when I called. The guy had a spare cover in his van - he collects the parts when he attends demolitions. So it was easy in the end.