He said his former party's claim that they had rescued the country from "Labour's great recession" was "the mother of all lies".
In a post on his website, author and historian Lord Skidelsky said: "The Great Recession was caused by the banks. Governments, the Labour government included, by bailing out the banks and continuing to spend, stopped the Great Recession from turning into a Great Depression.
"Yet practically everyone seems to believe that the Great Recession was manufactured by Gordon Brown."
He added that while the coalition government's austerity strategy had reduced the deficit, most economists agree the economy would have grown between 5% and 10% more in the past five years with "more sensible policies".
Lord Skidelsky was made a peer in 1991 and joined the Conservative party in 1992. He served as chief opposition spokesperson for Culture and for Treasury before being removed from his position by William Hague in 1997 for opposing the Nato bombing of Yugoslavia.
He left the Conservative party in 2001, and currently sits as a crossbench member of the House of Lords.
Lord Skidelsky said the Conservative narrative on deficit reduction and austerity had been so successful all alternatives were seen as "unthinkable".
"But sooner or later reality will break in," he said. "And what is now unthinkable will become sensible again. But not in this election."