Rail electrification cost 'significant disappointment'
The cost of electrifying the Great Western railway line between Cardiff and London could reach £2.8bn, the boss of Network Rail has said.
Chief executive Mark Carne told MPs the estimate had been £874m in January 2013 and £1.5bn in September 2014.
He said the "cost base was out of date" because significant electrification had not been carried out for 20 years.
Mr Carne also blamed "inadequate planning and scope definition of the project in the early stages".