Hold the switch so the button is facing up. Then put a small screwdriver into the hole at one end of the switch under the white strap and in the small groove and lift up. Do the same to the other end and it will come apart.
Single pole switches the Live
Double pole switches the Live and Neutral
The use of double pole switching guards against the dangers associated with a Live/Neutral reversal. In this circumstance a single pole would break the circuit on the neutral leg and the device would not operate HOWEVER lurking within would be the Live and the associated danger of electrocution. If both Live and Neutral are switched then this possibility is removed.
In summary so long as everything is wired correctly single pole will suffice but to guard against a Live/Neutral reversal double pole switching will always ensure safe disconnection.
Our UK plugs comply with the British Standard regulations BS 1363-1 - the specification for rewirable and non-rewirable fused plugs governed by The National Safety Standard of UK plugs.