Just to muddy the waters further however... I've read today that Suffolk Police are now saying that motorists WILL be fined if they have any snow on their roof:
"Police are warning motorists to make sure snow is cleared from the roof of their vehicles – or face a £60 fine.
Suffolk Constabulary said officers are taking action in extreme cases when the build-up of snow is a potential danger to the driver and other motorists.
Offences can result in three penalty points and a £60 fine.
The spokeswoman said: “We would like to stress that many people are not aware of the hazard that snow on their cars can cause.
“We would therefore encourage all drivers to take the time to clear their cars of snow and any ice, including the roof and bonnet as falling snow on the roads can be dangerous for all road users. Driver safety is our primary concern.” "
Which is it then? And... if I'm on the motorway and it starts snowing am I going to get in more trouble for continuing to drive with snow on the roof, or for pulling on the hard shoulder to push it off?
