Thank you all! Very good advice.
I have bought an energy meter reader that shows current energy flow from my flat.
I am suspecting that my water heater was not connected to the right circuit, as it heats up the whole day (I can see that my electricity use is nearly always high unless I completely turn the water heater off). I will try to invite an electrician over, as I am no good at those things.
Most of my light bulbs are LED (apart from maybe 4, but less often used).
I may also replace my storage heater in the living room as it gets a lot of electricity constantly, and takes at least 3 hours to heat the room. It is also because I live in a corner flat which is naturally much colder.
Thank you all – I will update you on progress in case this helps someone else!