To be fair, cutting chunks of carpet out could easily represent a safety hazard in itself - e.g. trip/snag hazard.But why oh why did they not just cut round the carpet even if they needed to ask my permission to do so? Though I still don't see what it has got to do with safety.
I don't think that the NCT testers will (or are obliged to) move clutter out of the way (e.g. in the boot or cabin) in order to perform their testing so there's absolutely no way that they're doing to start cutting carpet to get at the VIN even if the owner says it's ok!