Cable size on same circuit

Hello, looking to add 3 led lights for outside after contactor and see that lights already on the same circuit are wired in what seems to be 2.5m steel armoured. my question is whether it is ok just to add the new lights with 1.5mm t+e or is there another way which is better practice?

 

k then, at the moment there is i think 5 lights for a driveway- they are the victorian style of approx. 7/8 foot street light but do not know what size lamp they have and the furthest is 60m away from the board making me think that is why 2.5mm is used. can you also tell me please why for the contactor the live comes from the main power rather than the switch live of the timer as well as going to A1?

 

ok then, it has all made sense today thank you, i am just wondering now about the fact that some lights area already being supplied through 2.5mm but the new lights have .75m flex on them which cannot be taken out- is it still safe?
it all has a 10A MCB

 

because the cable goes underground down the driveway, this is with one buildings

 

doesn't matter, asked my boss earlier, he answered some questions, spoke to friend, doing it in plucky conduit, yeah they are outside a couple of doorways