How to measure amperate going through a 220V cable?
I may earn downvotes for this, but I would NOT recommend dealing with 230V when having no experience!

Anyway, of course it's possible what you want to do. Not the cheapest, but maybe the safest way would be using a current transducer like this http://www.lem.com/docs/products/lts_6-np.pdf
With that, you can pull the insulated phase wire through the hole, and get a voltage proportional to the current (the exact formula is in the datasheet) at the output to be measured by your Arduino.

Another, less risky approach without 230V:
A further indicator when the TV is off is when you push the "ON/OFF" button on your remote control.
It's most likely an RC5 or RC6 code. Connect an IR receiver to your arduino and implement a RC5 decoder to know whether one turns the TV on or off.