Drivers who rely on sat-navs are being warned to be extra careful as heavier speeding fines come into force.

From Monday next week (April 24), magistrates can dish out tougher penalties to motorists caught going well above the limit.

Fines will start from 150 per cent of weekly income rather than the existing level of 100 per cent.

It means, for example, someone who is sentenced for driving at more than 100mph in a 70mph zone will be dealt with in a more severe bracket.

MORE: Speeding laws are changing in April 2017: This is what you need to know about the tougher penalties

The changes could particularly affect drivers who rely on navigation devices, with a survey finding one in six drivers have been told the wrong speed limit by a sat-nav.

More than half the 1,783 UK driving licence holders surveyed did not know the correct speed limits for single and dual carriageways.

A third admitted they "rarely" update their sat-navs, making them more likely to be given out-of-date information.

Rod Jones, insurance expert at price comparison firm uSwitch, which commissioned the poll, said: "We are officially a nation of sat-nav junkies, but our addiction to technology is causing us to drive dangerously and risk large fines.

"While sat-navs and smartphones are an incredibly useful tool for motorists, it is important to remember they are never a complete substitute for knowing the rules of the road.

"Tougher penalties have already been introduced around handheld device usage that could mean newer drivers losing their licence after a first offence, and for all drivers the penalties have increased.

"Drivers will be hit even harder for speeding when the new, heavier fines come into effect next week."