There are several very large signs in the lounge warning you that luggage is only to be stored in the lounge while you use the facilities. While I suspect you get geyt away with nipping out for an hour or two, all day probably won't worl. They do note down what flight you arrive on and it would be easy to calculate how long you have been there. 6 hours plus - and if you don't respond to a PA call - and you can expect your bags to be confiscated by the police and possibly blow up as a suspect package.

As Globaliser says - use the left luggage office.