This is a list of road, railway, waterway, and other tunnels in the United Kingdom. A tunnel is an underground passageway with no defined minimum length, though it may be considered to be at least twice as long as wide. Some government bodies define a tunnel as 150 metres (0.093 mi) in length or longer. When completed, the Chiltern tunnel will be the 2nd longest mainline railway tunnel in the UK at 16.04 km (9.97 miles). As of 25 Nov the TBMs had bored over 7km.