Voltage issue with led lights

[Nigel111]

Hi Problem: I have 5 (240v) led lights in a bedroom on a single on/off switch (not dimmer) and all the leds worked fine until last w/end. Then with the switch being off, the leds would flicker/strobe. Switch on and they all work fine. Disconnected the switch completely and still the same flickering issue. Found that the (switched) live goes into an inaccessible junction box(call it no 1) from which a 1.5mm cable seems to go to the bedroom ceiling and ends up in another junction box (call it no 2) where all 5 leds then connect. So, disconnected all the leds in this box 2 and found that there is 12v across the live and neutral at the incoming 1.5mm cable. How do I solve this...can I connect something across the 1.5mm cable in this box 2 that will stop the leds from flickering? Thanks for any guidance/links. Nigel