Opening up the countryside for ramblers has cost £69m - double the original estimate of £28m - a Parliamentary watchdog has revealed.
Thousands of acres of land have been opened up to walkers
The National Audit Office (NAO) said the Countryside Agency under-estimated the amount of work needed to produce maps of the newly-accessible areas.
But it praised the scheme overall, saying it was "implemented well".
The scheme opened up nearly two million acres of previously off-limits land, away from footpaths.
The NAO criticised the Countryside Agency for not using a pilot scheme to judge costs.
But overall, "right to roam" in England and Wales had succeeded, it said.
The agency said a pilot would have helped to judge costs but a "very tight" government deadline to introduce the scheme had ruled that out.
'No more restrictions'
It is high time public bodies stopped leaping into the dark when undertaking projects
Edward Leigh MP
Chairman, Commons Public Accounts Committee
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Sir John Bourn, head of the NAO, said the scheme had generally been a success because "walkers are no longer restricted to existing footpaths across large areas of the countryside".
"Although the scheme's implementation has gone well, the Countryside Agency should have put effective risk and project management procedures in place earlier," he said.
The Commons Public Accounts Committee, which reviews the NAO's reports, was critical of the way money had been spent.
The committee's chairman, Conservative MP Edward Leigh, called it an "unsightly blot on this newly-opened-up landscape".
"It is high time public bodies stopped leaping into the dark when undertaking projects, knowing that the long-suffering taxpayer will have to pick up the tab," he said.
Andrew Wood, landscape, access and recreation direction for the Countryside Agency, told BBC News if a pilot had taken place the government's December 2005 target to introduce the scheme would "never have been met".
But it was "probably true" a pilot would have shown the true costs, he added.
The costs had been far higher than estimated "simply because nobody had ever done anything like this before", he added.
"This was a huge exercise - nobody had tried to map these open areas for this sort of purpose," said Mr Wood.
A "large number of appeals" from landowners against some designations had added "difficult to anticipate" costs, he added.
The NAO report made several recommendations to the agency, including improving its website and encouraging people on low incomes and from urban areas to exercise the new right.
Open access was introduced between September 2004 and October 2005, ahead of the target of December 2005.
The NAO said it was too early to measure the take-up of the new right in a meaningful way.
But in 95% of the NAO's visits to sites there was easy access to the land, and it was possible to walk across land without obstruction in more than 90% of cases.