Inside the Eurotunnel service tunnel on its 20th anniversary

Tuesday marks the 20th anniversary of the opening of Eurotunnel, the passenger and freight rail link between the UK and France that runs deep beneath the English Channel.

The tunnel cost £4bn more than its estimated budget, was finished a year late and almost went bankrupt less than 10 years ago, but is now turning a profit.

Between the passenger trains and the drive-on vehicle shuttle services, an estimated 20m people used the tunnel in 2013.

Transport correspondent Richard Westcott was given access to the service tunnel that runs between the two main tunnels, 40m (130ft) under the sea bed.