A referendum on changing the voting system cost taxpayers £75 million, an election watchdog said.
Official estimates made in the run-up to the national poll suggested the final bill would be around £100 million, a figure often quoted by opponents of the alternative vote reforms during the bitter campaign battle.
But fees and charges for running the vote were much lower than expected, according to the Electoral Commission.
Jenny Watson, who chairs the commission, said: “The public have a right to know how their money is spent at major polls, and we’ve been able to set this out for the first time today.
“These figures show the Government’s original estimates of the cost of the 2011 referendum were too high by more than £20 million so it’s important that lessons are learnt.”
Voters decisively rejected the Liberal Democrat proposals to introduce the alternative vote system in May last year.
The Electoral Commission called on the Government to publish full details of the European Parliamentary elections held in 2009 and the 2010 general election as well as the recent police and crime commissioner elections.
