Security lighting should be hard wired through a fused spur (preferably switched), taken from your ring main. Up to the spur the cable should be 2.5 mm twin & earth cable. After the spur and feeding the light the cable should be 1.5mm twin & earth.
Twin and earth cable should
not, must
not, be wired into a 13 amp plug! A 13 amp plug is designed to be used with flexible cable.
For your own and your families safety I will repeat:-
Get a qualified electrician to install the security light.