Well it works very nicely over HDMI to the main house telly, not a soss via composite to the ickle telly.

Have seen something suggesting composite is suppressed if HDMI is detected, but just whipping the HDMI plug out doesn't get it to switch if that was the prob.
The config.txt has an "uncomment this for composite" but it wouldn't let me edit it - I assumed the SD card had the write protect on but maybe I just need to sudo.
Or it might be something else!