The speed limit would be introduced as part of the planned upgrade to the M1 in South Yorkshire and the East Midlands and would apply between junction 28 at Mansfield and junction 35a at Sheffield and Rotherham between 7am and 7pm, seven days a week, as part of improvements planned for the M1.

However, the RAC has warned that the speed limit could form part of a blanket lowering of motorway speed limits.

The speed limit will be used to manage traffic speeds and help reduce congestion and air pollutants locally.

The plan forms part of the ‘smart’ motorway scheme under which the hard shoulder would be used as a permanent running lane supported and controlled by variable mandatory speed limits to manage traffic and reduce congestion.

The proposed maximum mandatory speed limit would work in parallel with the variable speed limits which would be set as part of the congestion reduction measures for smart motorways.

In response, RAC technical director David Bizley said: ‘This is a landmark proposal as to the best of our knowledge motorway speed limits have not previously been lowered in order to comply with environmental legislation.

‘If this becomes reality for the 34-mile stretch of the M1, which seems highly likely, it would certainly negate some of the current benefits of operating this section as a 'smart' motorway where motorists are allowed to use the hard shoulder to reduce congestion.

‘More worryingly, it could pave the way for similar restrictions on other sections of motorway. While preserving air quality is obviously a paramount concern there will inevitably be a negative impact on business efficiency and individual mobility.

‘This very powerfully demonstrates the impact that speed has on emissions and many will be surprised to hear that a reduction of just 10mph can have such a significant effect on improving air quality.’

Roads Minister Robert Goodwill said: ‘No decision has been taken to impose speed restrictions on the M1. Any speed restrictions to improve air quality would be temporary, only ever considered as part of road improvement work and would not be appropriate for the vast majority of projects started in this Parliament.

‘We are funding significant improvements to the road network to tackle congestion and support the economy. Smart motorways mean more lanes for drivers, freer-flowing traffic and quicker journeys.

‘We need to ensure that, as we invest, we are alive to instances where there could be a negative effect on air quality.’