The residual current circuit breaker
The residual current circuit breaker (RCCB)
After the isolator the live and neutral go to the RCCB, or trip switch. It protects the people in the house from electric shock: if current leaks to an appliance's metal case or to the ground, or too large a current flows, it switches the circuit off automatically. It too is a double-pole switch.
Figure to be added
An ordinary switch is on when its lever is down; this one is on when its lever is up.
Why one wire is live
One wire is earthed at the step-down transformer, so there is 230 V between the other wire and the ground. Touching that unearthed wire from the ground puts 230 V across the body: a shock. A current of 50 mA through the body is a severe shock and 100 mA can kill. That wire is the live; the earthed one is the neutral.
This is what lets the RCCB work. Working by electromagnetic induction, it cuts the whole house off when about 35 mA leaks to earth anywhere, and also when about 30 A flows into the house. It may trip in a lightning storm, but it does not guarantee protection from lightning.