Variable speed limits will soon be imposed on the M20 in a bid to cut congestion and carbon emissions.

The Highways Agency this week revealed it is pushing ahead with plans to impose the limits between junction 4 (Leybourne) and junction 7 (Detling).

Once the scheme is in place, motorists have to check electronic signs above the motorway lanes for the speed limit - which will still be a maximum of 70mph.

It will be enforced with speed cameras. A similar scheme is already used in some parts of the M25.

The area was chosen because "Maidstone has suffered from peak-time congestion problems for some considerable time", the report said.

Motorists were consulted on the plan through the Highways Agency website last year. Just 73 people responded, with 41 of them in favour.

Of those against, most expressed concern that variable limits do not work on the M25 and that the scheme would need increased police patrols to work.

Others suggested that money should be invested to control foreign vehicles on the M20 instead.

But variable speed limits have been backed by Maidstone council, Tonbridge and Malling council, and KCC. Supporters of the scheme said the main benefit would be reduced noise.

A Highways Agency spokesman said: "Controlled motorways are designed to smooth traffic flows and make journeys more reliable by reducing the stop-start effect of traffic during busy periods.

"A controlled motorway also has a positive impact on the surrounding area by reducing noise and air pollution from the road.

"The M20 Junction 4-7 controlled motorway scheme went to public consultation last summer. The response to the consultation was largely positive, so we are taking the scheme to the next stage.

"We will make an announcement in due course."