Calico, you have something seriously wrong. Before you do anything check the meter and write down the reading. Check it say 1 hour later and write down the reading again and the time. Then check the difference between the readings, for your hourly rate of use.
Then turn off and/or plug out EVERYTHING in apartment, including the cooker, fridge (it won't cool down much' if you don't open it) clock-radio, TV, computer, immersion etc (btw TVs, DVDs, computers may be on standby and draw power, even if turned off - Plug them all out!!) Check you meter, write down the reading and time.
Your meter should be stopped. Dead. Not moving.
If it isn't check everything again until you're sure that there is NOTHING left on. If the meter is still going then either you've got some hidden item drawing power or another user is hooked up to your meter.
On the other hand if the original 1 hour check shows a very high difference, then you may have something eating electricity, e.g. dual immersions can do that if the thermostat is kaput, or if the bath selection is on. Switching things on/off one by one can help suss out the culprit.
You can also use [broken link removed] from Maplins. Do all the plugging out still though.