Unblocking a basin
If your basin gets clogged, don't panic - try using a plunger. Keep a damp rag over the overflow while you do it. If the problem persists, contact a Master Plumber.
If you're on mains water, the most important thing you need to do is find out where the water shut-off valve is and how to turn it off. It's often under a lid close to the property boundary. If you're on a pumped water supply, know where to isolate the power to the pump and how to turn the water off at the water tank.
Knowing how to turn off your gas supply can also be important in an emergency. This is usually done by turning off the valve at the inlet to the gas meter or, if you're on LPG, at the taps on top of the bottles.
In all cases, if you can't find it or don't know how to turn it off, contact a Master Plumber.