That is a BIG NO NO !
and if you have to ask ,you should seek out professional help.
and your current light switch controlling the lights should be a double pole switch anyway ,preferably a switched fused spur
Not if its off a lighting circuit it doesn't, single pole is absolutely fine.
The real issue is the wattage of the outside lights, if they are stonking halogen jobs then they will exceed the rating of the lighting circuit.
Agreed you need a fused spur (plus appropriate rated fuse) with isolator if they are fed from a ring main to provide the correct upstream protection.
It's an outside light ,so special location, requires double pole isolation from the lighting circuit which someone decided to connect it to,
fused spur is a double pole switch
if the outside light is powered by a plug (with correct sized fuse),which can be removed from a socket *with RCD protection (thus giving double pole isolation) it is effectively a portable appliance, not notifiable.
in this case, the lighting circuit is RCD protected ,(from what the OP said)
However, not all installations are up to date ,dual RCD consumer units or better.
some are ye olde wylex re-wirable antiques with no RCD or even decent overcurrent protection
I have two outside security lights fed from a single pole switch in the kitchen, on the lighting circuit. The are 10W leds.
so when water gets into your cheap Chinese LED security lights , how do you isolate them ? assuming your still alive ?
are your lighting circuits RCD protected ?
you'll need a torch to see to reset the RCD because it will have taken out your lights too (if night time ,but such problems rarely happen in daylight or at convenient times)