Rail upgrade costs in numbers
A £1.2bn hike in the cost of the Great Western Main Line rail electrification is "staggering and unacceptable", the Public Accounts Committee has said.
The cost of upgrading the line between Maidenhead and Cardiff was set at £1.6bn in 2014 but is now estimated to cost £2.8bn.
The line from London to Oxford and Bristol Parkway was originally due to be electrified in 2016, to Cardiff in 2017 and Swansea in 2018.
Ben Thompson goes through the numbers.