An external socket should be either IP 56 or IP 55
They have lids...
http://www.rainfordsolutions.com/ip-enclosure-ratings-and-standards
It's a neat idea to have some kind of isolator switch on the inside to disable the external socket - Amazon will sell you one.
If you're concerned about the building regulations then have a sparky do the work properly.
Dvoid of any good wishes...
June 2017