Helmet Camera Advice

How good does the recording have to be??

You could just get 1 these at £25 +pnp, with up to 10hrs capacity but 2hrs life per charge:
http://www.dogcamsport.co.uk/ds3-chewing-gum-camera.html

Or get 3 for the full 6hr ride

Id say for that requirement you need to be looking at a decent camcorder and a remote bullet cam at least, with a lot of spare batteries for both. You put the camcorder in your backpack and the bullet camera goes on the helmet with the cable running down to the bag. With this setup you could also mount the camera in different places, facing forward or backward or even mounted on the bike.

For a good example of what you need lookup some of what was used to film Marc Beaumont's ride through america. Pic here (there is a video of him explaining it somewhere, perhaps on the BBC webpage for the series)

http://www.flickr.com/photos/cyclingtheamericas/3738220502/

http://www.flickr.com/photos/cyclingtheamericas/3738224074/

Found the good one, ouch, expensive!

http://www.actioncameras.co.uk/VIO_POV.1.5.html

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DogCam do the POV.1.5 at £50 cheaper...
Or get one of their minidvr2 systems @ £165 and buy a bunch of batteries.

http://www.dogcamsport.co.uk/mini-dvr-2-helmet-camera.html