This scheme required two additional sections to join what were two different schemes, from Swanley to Sevenoaks in the south-east and Hunton Bridge to Potters Bar in the north-west. The section of Ringway 3 west of South Mimms anti-clockwise around London to Swanley in Kent was cancelled. The section from Potters Bar to the Dartford Tunnel was constructed in stages from June 1979 onwards, with the final section between Waltham Cross (Junction 25) to Theydon Garnon (Junction 27) opening in January 1984. This section, running through Epping Forest, attracted opposition and protests. In 1973, local residents had parked combine harvesters in Parliament Square in protest against the road, draped with large banners reading "Not Epping Likely". As a consequence of this, the Bell Common Tunnel that runs in this area is twice as long as originally proposed. The most controversial section of the M25 was that between Swanley and Sevenoaks (Junctions 3 to 5) in Kent across the Darenth Valley, Badgers Mount and the North Downs. An 1800-member group named Defend Darenth Valley and the North Downs Action Group (DANDAG) argued that the link was unnecessary, it would damage an Area of Outstanding Natural Beauty and it would be primarily used by local traffic as a bypass for the old A21 road between Farnborough and Sevenoaks. After a length inquiry process, chaired by George Dobry QC, the transport minister Kenneth Clarke announced the motorway would be built as proposed. The section from the M40 motorway to the 1970s North Orbital Road construction (Junctions 16 to 17) opened in January 1985. The route under the Chalfont Viaduct meant the motorway was restricted to a width of three lanes in each direction. The Prime Minister Margaret Thatcher officially opened the M25 on 29 October 1986, with a ceremony in the section between Junctions 22 to 23 (London Colney and South Mimms). To avoid the threat of road protesters, the ceremony was held a quarter of a mile from the nearest bridge. The total estimated cost of the motorway was around £1 billion. It required of concrete, of asphalt and involved the removal of of spoil. Upon completion, it was the longest orbital motorway in the world at . At the opening ceremony, Thatcher announced that 98 miles had been constructed while the Conservatives were in office, calling it "a splendid achievement for Britain". A 58-page brochure was published, commemorating the completion of the motorway.