I've read here that clamp meters are about 5% accurate, so if I bought one like this for £20 (+vat+postage)
Data hold and peak hold functions
DC Voltage: 1V - 1000V (±0.5%) AC Voltage: 1V - 750V (±0.6%) AC Current: 0.1A - 1000A (±2.0%) Resistance: 200 ohms - 20k ohms (±2%) Insulation test 2000M ohms Max. Max. display 1999 Jaw Size 58mm