Can't think of the names of bits..

When i turn the key in the lock to lock door, first turn locks door, but if i turn it again i get a red flashy light come on by the plunger on the drivers side door.

What does this light mean?

It means that the deadlocks are activated. Usually it should be one key turn for the deadlocks and 2 turns to deactivate them. I think that the convenience system has been re-code so that they work in the way that you describe. With the deadlocks on the door cannot be unlocked from the inside, so as if someone were to break a window they won't be able to get the door open.