How to assess electic devices for overusage?

You really need to provide more information.

If your electricity consumption has suddenly doubled(without you having new appliances) it must be something major. Like the immersion heater on all the time, freezer/fridge compressor running all the time(door open?) a neighbour stealing your electricity(has happened)

You can buy devices to monitor consumption or simply switch everything off and then switch on one at a time and simply look at the meter.

Yes, I bought something similar a few months ago - gives you an idea of what's using the most energy.

I too are with Powergen, and also had a strange jump in consumption. I just hope you're a patient person. I've been trying to sort this out since October last year (and I've really been pestering them!), and I've still not sorted it out.

A word of warning, a lot of the customer service staff don't appear to be trained for such enquires, and you'll probably be made to go down various avenues before getting on the right road. Unfortunately, there's not a lot of advice I can give as to sorting out quickly. You just have to hope that you get someone with knowledge about it early on.

They will probably try to change your meter, but as I found out from the guy who came to change mine, you have to have a load test done on it first (which they won't to do as it costs them money) or you can't prove the meter was faulty and have no leg to stand on if you want to get your money back.

Aparently the department who deal with these consumption disputes are over worked at the moment and that is why it takes so long. (they'll tell you anything!)