The UK government did not do its own analysis of the cost of the biggest reorganisation of councils in England for decades, the BBC has learned.
Deputy Prime Minister Angela Rayner said "a significant amount of money" could be saved by merging councils in 21 areas into single authorities.
Rayner's department, the ministry of local government, based its cost estimates on a 2020 report commissioned by the County Council Network (CCN) that said £2.9bn could be saved over five years.
But the CCN has since revised its analysis and now says the reorganisation could make no savings and actually cost money in some scenarios.
Tim Oliver, chairman of the CCN, said local government reorganisation "could unlock billions in efficiency savings to be reinvested in frontline services", if it was delivered at the right scale.
Oliver said the CCN supported the government's reforms but added: "We are concerned over the potential costs of reorganisation where proposals seek to replace the two-tier system with multiple small unitary councils."
It just keeps coming….