I would say the best idea would be if you signed up as a developer at the NavTech site yourself and downloaded it. I'm pretty certain that the licence agreement will say that rcldesign isn't allowed to disclose the format infromation to third parties. Otherwise they wouldn't have made him sign up to be able to download it would they!
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(list 6284, Mk1 S/N 00299 4GB blue [sold]. Mk2 S/N 080000094 20GB blue)