Beware tinted car windows, in-car navigation systems and driving your motorised wheelchair at more than 8mph on the road.

These are the new scourges for the modern-day driver identified in proposals for an updated Highway Code, the road-users’ bible.

Following parliament’s decision last week to outlaw smoking in public places, motorists will also be told for the first time that smoking at the wheel is a potential distraction which might cause them to crash.

The code, which was last amended in 1999, is one of the biggest selling non-fiction books in Britain, with about 1m copies purchased each year. A revised edition is due to be published in the spring of 2007.

Ministers claim the changes — which went out to public consultation last week — reflect emerging trends on the nation’s highways, legislative reform and recent advances in technology. But critics believe some of the new advice may be driven by political correctness and a nanny state approach.

Proposals include the addition of a “diversity statement”; a suggestion that drivers on long journeys should drink two cups of coffee and have a catnap of up to 15 minutes if they feel tired; and “green” advice to reduce harmful emissions by switching off the engine when a car is stationary.

“When the code was launched in 1931 there were just 2.3m vehicles on the roads and today there are over 30m,” said Stephen Ladyman, the minister of state for transport. “It is essential reading for everyone who uses the roads.”

The advice on satellite navigation — or sat nav — systems proposed by the Driving Standards Agency (DSA) says: “There is a danger of driver distraction being caused by in-vehicle systems such as route guidance and navigation systems . . . Do not be distracted by maps or screen-based information (such as navigation or vehicle management systems) while driving.”

The proposal also warns against drivers being lulled into a false sense of security by other technological innovations: “Do not rely on driver assistance systems such as cruise control or lane departure warnings. They are available to assist but you should not reduce concentration levels.”

More than 2.2m vehicles are now equipped with a sat nav system, according to a government estimate. A fifth of new cars have the systems fitted as standard, but the majority of sat nav units are bought “off-the-shelf” in shops such as Halfords and Dixons. About 1m of these units are thought to have been sold in 2005 alone.

Sat nav systems rely on a global positioning device which receives a satellite signal to track a car’s movements. Drivers punch in their starting point and destination and the quickest route is automatically plotted on a screen. An automated voice can provide instructions on some units.

New research by Privilege insurance will show this week that almost one in five motorists (19%) admits losing concentration while fiddling with the sat nav unit during a journey — 2% more than drivers who fumble with conventional road maps.

Another addition to the Highway Code proposed by the DSA may disappoint criminals and celebrities keen to hide their identity behind blacked-out windows. “You MUST NOT use a vehicle with excessively dark tinting fitted to the windscreen,” it says.

Under existing laws to ensure clear visibility, all windscreens must allow in 75% of the light, 70% for side windows. These standards are maintained by vehicle manufacturers, but police are concerned about a growing trend for darker tinting film added to cars once they are on the road.

Last year Gary Neville, the England and Manchester United footballer, was reportedly fined and forced to change the windscreen of his car because it was too dark.

The revised Highway Code will also feature a new section on powered wheelchairs and mobility scooters, under the DSA proposals.

The move follows a spate of accidents involving elderly or disabled people — nicknamed “hell’s grannies” — driving their motorised wheelchairs in a reckless manner.

In 2004 seven people were killed, including a woman who reversed off a pier into the sea and a man who was run over by a wheelchair painted in the colours of Ferrari.

The speed limit for motorised wheelchairs and mobility scooters is 4mph on the pavement and 8mph on the road.

Additional reporting: Ed Habershon