Britain's busiest motorway is 25 years old tomorrow - and still as controversial as ever.

Those in favour of the 117-mile M25, such as Roads Minister Mike Penning, reckon the London orbital road has changed lives for the better.

But those opposed say that all it has done is attract more and more traffic - a view possibly shared by the many Londoners caught in the road's notorious jams every day.

First suggested as far back as 1905, the first part of the road opened in September 1975 with the final 13-mile section being opened by the then prime minister Margaret Thatcher on October 29 1986.

There was even talk of the M25 being only two lanes wide at one stage but it opened with three lanes in each direction, with various widening schemes introduced as the years went on, with the widening still going on.

The section to the west of London around Heathrow airport is the busiest part of the M25. When it opened, around 113,000 vehicles a day used this part.

Now the figure is around 200,000.

The M25 has 13 junctions and 234 bridges, including the Queen Elizabeth II Bridge at the Dartford-Thurrock River Crossing which was opened by the Queen on October 30 1991.

The route was subject to no fewer than 39 public inquiries lasting a total of more than 700 sitting days.

The inquiries led to the doubling in length of the tunnel at Epping Forest in Essex and extensive cuttings near Swanley and Sevenoaks in Kent to shield an Area of Outstanding Natural Beauty.

In total two million tonnes of concrete and 3.5 million tonnes of asphalt were used during construction. More than 2.1 million trees and shrubs were also planted.

The full motorway construction at the time cost £909 million over 11 years, or roughly £7.5 million per mile.

Mr Penning said: "Since opening in 1986 as a major engineering achievement, the M25 has changed our lives for the better. It has transformed the way we travel around the capital, and helped hauliers from across the UK and the continent to connect different parts of the country.

"With Government investment, the M25 will continue to evolve and support the economy, introducing additional capacity to better manage traffic flows through activities such as widening and hard-shoulder running."