Former Tory chief George Osborne has claimed he was opposed to Universal Credit while he was Chancellor.
The ex-Tory MP, who was part of the Cabinet which introduced not only the welfare changes but a series of brutal cuts to public spending, has now claimed he "didn't think" it would work.
He also accused Boris Johnson of being a Jekyll and Hyde figure - betraying his liberal beliefs to get himself to the top of politics greasy poll.
Quizzed by former Scottish Tory leader Ruth Davidson about the Universal Credit changes, Mr Osborne said: “I didn’t think Iain Duncan Smith’s plan would work and I’m yet to be convinced that it will.”
But allies of Mr Duncan Smith accused Mr Osborne of trying to rewrite history - pointing out that the he resigned from the government over Mr Osborne's plans to implement a further £1billion in cuts.
As Chancellor, Mr Osborne cut £4billion out of Universal Credit, which many critics say killed off any chance the scheme had at success.
Universal Credit is a benefit for working-age people, replacing six benefits and merging them into one payment.
It was designed to make claiming benefits simpler.
But it has been plagued with errors since its roll out began - with people losing money and being forced to wait a long time for payments.
The National Audit Office, which oversees government spending, said that the universal credit programme was "driven by an ambitious timescale" and that it had suffered from "weak management, ineffective control and poor governance".
The Resolution Foundation warned that cuts to the benefit have weakened its core purpose - to make it more attractive to work than to receive welfare.
The former top ally to David Cameron also called Boris Johnson "a contradiction" and accused him of supporting Brexit "to get himself to the top".
He said of Boris Johnson: "He is enormously entertaining and engaging and also a contradiction.
"He's a very talented, in many ways brilliant, political operator.
"But often he'll adopt causes to get himself to the top that I don't agree with, including Brexit."
He continued: "I always think when I look at Boris... I think he's got what it takes to be prime minister and he clearly fills the job, but I kind of wish he was the half of the Boris, the Dr Jekyll side of Boris Johnson.
"Which is the liberal, tolerant, pro-immigration, centrist Tory who was so successful in this city, London.
"Not the Mr Hyde who is divide the country, push Brexit to its political limits in order to eke out the advantage amongst the Brexiteers."
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