Just to check, it shouldn't be drawing a charge when connected to the hub but nothings plugged in should it? It's just the light output from my revo is much lower with the unit plugged in than not and it makes me think there might be an issue with mine. Without I can light all four lights on the roll downhill by my house, with its not doing that even if I'm pedalling as well.

Does anyone round Shrewsbury way have one that works that I could try out to check?

I have my light/c2c on all the time. Any half decent pedalling effort and it's lit up fine. Even when charging my phone/GPS and light on at night it's good enough.

How's it wired? C2C and Revo wired in parallel straight from the hub?

Yep. In parallel both off the hub connector. I've disconnected the C2C at the stem cap and the revo works fine, plug it in and I struggle to light up 4 leds. Suggests it's not the connection or a fault in either cable.

I was going to fit a switch but it seems daft to do it for a non working unit.

Mine developed this fault/situation after a very wet multiday ride.

I fixed it by removing it! But would be interested in a more useful solution

Yeah, sounds like the unit is drawing a charge ... probably worth an email.