Dont forget that neutral is specified as a LIVE conductor. SP generally OK for sockets (and lighting!)
There are some places where double pole is required (or specified):
Cooker switches
Switches for electric showers
Isolation switches feeding boilers
Isolation switches feeding domestic appliances (eg washing machines) - many appliance maint men wont work on appliances unless they can be fully isolated.
You may see more of this in 17th Edition when they've finished putting the gold leaf on the edge of all the pages.
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