Hello, I have worked in on site meter testing for 10 years after queries were raised re high powerbills.
Most common problems were:
1. Misreading of the meter, especially the clockdial meters get misread quite often especially when near the 9 and 0.
2. Faulty hotwater cylinder thermostat or valve leaking and water straight out of the overflow pipe.
3. No access to meter, guessed readings by meter reader and perhaps a correct reading was obtained and a catch up in true usage because of underestimated readings.
4. Meter accuracy is in general very good and most meters are well within class 2 and often within 1% accuracy and not the cause the problem. The 5 or so fast meters I struck like 200% fast were:
One electromechanical meter where the brake magnet failed after a lightning strike nearby. Also there was a lot of damage on appliances.
The others were electronic meters where circuitboard electrolytic capacitors failed.
From my experience the mechanical meters are a lot more reliable and accurate long term than the electronic rubbish they try to install.