I think that unless you have a letter from your local force stating that the machine is legal without lights then a police officer can use his discretion and report you.
At the end of the day all he has to say is that in his opinion the road conditions dictated that a dipped headlight should have been used and you didn't have one fitted, so you were therefore a danger to yourself and other road users.
I ran a ducati years ago with a daytime mot but I certainly wouldn't chance it now. Too many rules and regulations.
