The first phase of the HS2 high-speed railway between London and Birmingham could see an extra five year delay, according to the Minister of Transport with the line now set for completion in 2031 – from its original 2026.
Transport Minister, Grant Shapps, said: "I want the House to have the full picture. There is no future in obscuring the true costs of a large infrastructure project - as well as the potential benefits".
The route - from Birmingham to Manchester and Leeds - was due to open in 2032-33, but that has been pushed back to 2035-2040.
HS2 Chair, Allan Cook, said the delay is due to the original plans not accounting for the effect of building through densely-populated areas with difficult geographical features.
Originally expected to cost £56bn in 2015 prices, Mr Cook said the new cost estimate was adjusted for inflation, and based on today's prices.
Last month Mr Cook told the Department for Transport that the scheme could not be delivered within its budget.
HS2's total cost has also risen from £62bn to between £81bn and £88bn.
The second phase has also been delayed.
The first trains are unlikely to run until 2028 - while Manchester and Leeds won't benefit from services until at least 2035.
