Logically... what would anyone do if their headlight was broken by a stone while travelling on the road in daylight? Stop and order a recovery transporter? I certainly wouldn't.
Surely daytime in good light conditions is OK. Be wary of the 'lights-on' till one hour after sunrise and one hour before sunset Road Code strictures, though.
Surely Direct Line know... and they did say you could quote them.
A quick google around the web isn't sufficiently helpful, I found. Though you might find better.
Contact the police, explain your situation and ask them?? Though it may be unclear in law. Common sense should rule but sense isn't always that common, eh. And when it comes to the letter of the law, depending on the officer... it can sometimes be frustrating.
All things considered you're probably OK in good daylight conditions.