More than £8 billion will be added to the bill for HS2, as the cost of trains has not been included in widely publicised figures.
The cost of the high-speed rail line has been quoted as £33bn but a question tabled in the Commons has revealed a further £8.15bn will need to be spent on trains.
The Government said the cost of a new fleet of trains had been revealed last year.
However, leading campaigners accused ministers of being 'totally disingenuous'.
Spending on HS2 is forecast to soar above £366m in this financial year and reach £422.5m in 2014-15.
Stop HS2, the main opponents of the two-phase project, say total spending will top £1bn before a vote is even taken on the scheme in 2015.
Phase one of HS2 will link London to Birmingham, passing through Whittington in Staffordshire. The second phase, which extends to Manchester, will cut through large parts of Stafford and Stone countryside, including Great Haywood, Ingestre, Hopton, Marston, Yarlet and Swynnerton.
Joe Rukin, Stop HS2 campaign manager, said today: "It has been totally disingenuous that the Government has been quoting a £33bn cost for HS2 while neglecting to mention that trains are an extra."
He said compensation payouts would increase the bill further.
The Department for Transport today said it had been 'totally clear and transparent about the costs of HS2'. A spokesman said: "Capital costs for the construction of the vital project are in the order of £16.3 billion for phase one and £16.8 billion for phase two, not including the spur to Heathrow. If the spur is included, phase two would cost in the order of £18.2m." She said there was a separate budget for rolling stock.