Replacing outside light?

I want to replace an outside ordinary external light with a pir controlled spot/security light I am conversant with electrics and able to carry out the work but want to know if because it's an external light do I HAVE to get a registered electrician. I done several prior to the regulations on my previous houses and one on our current abode and all tested by electrician friend, results ok and shown to be safely installed more so than the front door lantern supposedly installed by electrician many moons ago metal rotten he used iternal twin flex and no earth changed that to twin and earth and new light earthed.

Don't ask me to ask my pal that would be difficult his ashes are floating in the channel [ex Electronics officer RN. 26yrs burried at sea].