yes you would have to feed a new cable to the proposed outside light
a light requires live and neutral to work,however the switch only has lives passing through it. as you can hopefully see you would need to supply the new light with a neutral so that when the switch is toggled the lamp will light
edit
re -read your post and as you no longer want the 2nd light(on switch) if you can disconnect these cables within the light fitting and re-run them to the new light position then robert is your mothers brother...etc
OK, i have opened the light fitting up and connected the Black, Red and Earth to the black red and earth that used to be connected to the switch (taking the red sleave off the black from the light fitting). The Three wires that used to be in the switch are now feeding the new outside light. The light is now working.
I now want to replace the double switch as only one of the switches are now needed. Within this switch that is controling the upstairs light is a Red, Black, Yellow and Earth. Where would these wires go in a single switch.
Thanks