National Highways Regional Director Nicola Bell said: “Our road network is an integral part of our customers’ journeys and the backbone of the country’s economy; it connects people, builds communities and helps people go about their daily lives.

“Our primary concern is always safety, but changing speed limits before any incident creates a much greater risk for the general traveling public. “

Police chiefs came under fire last week after videos appeared to show officers facilitating protests rather than arresting activists.

The activists who were arrested simply returned to block the road again as soon as they were released.

Police are said to be reluctant to prosecute activists for relatively minor offenses, such as blocking the highway, as the penalties available are unlikely to have a deterrent effect.

Instead, senior officers in Hertfordshire, Surrey, Kent, Essex and the Met looked to see if they could lay more serious charges, including conspiracy to cause public nuisance.

Roger Hallam, the mastermind of Insulate Britain, is hoping that dozens of activists will be jailed ahead of the COP26 summit in Glasgow in November, in order to humiliate Boris Johnson, it has been claimed.

The Extinction Rebellion co-founder reportedly told his supporters earlier this year: “The whole world is going to look at Johnson and say ‘You are Mr Green and you have 200 people in jail because they want you to isolate them. A few houses. ? ‘ It’s not going to look good.

Insulate Britain demands that the government “immediately pledge to fully fund and take responsibility for insulating all social housing in Britain by 2025”.

A spokesperson for the Metropolitan Police said: “We consider their actions to be an unreasonable and dangerous obstruction of the road and we will respond as quickly and vigorously as possible to any incident of this nature.”