The cable gives me  red and a blue and a yellow wires all connected to the switch and there is a bare cable not connected.

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You probably have a live, switch live and an earth at your switch. In which case you would need to get your supply from the nearest light (preferably from the last light in the circuit). You could either take this supply to your new light first and run another cable from there to the switch that you mention, or run it to the switch first and then run another to the light (this method requires you to put both neutrals in a 5a connector block). You can then put a 2 gang switch in place of your 1 gang. Dont forget to brown sleeve the conductors which are going to be live as well. Does this switch your talking about have surface plastic trunking going to it? This job would be easier if so but a bit more involved if not. To answer your question though, it doesnt sound like you can do what you have asked, so all this would need to be done by somebody who is qualified to do so.