Tory big beast Ken Clarke has urged George Osborne to hold firm on cuts to tax credits despite fears of a backlash from voters.
The former Cabinet minister admitted the changes - part of a package which will see a new £7.20 living wage introduced for over-25s - would be "unpopular" and have unpredictable effects.
But he insisted the current system is "subsidising low pay" and reform is "essential".
The comments, on the BBC's Andrew Marr show, come amid growing pressure on the Government to lessen the impact of the welfare cuts on working "strivers".
Mr Clarke said: "My advice to George is put your tin hat on, get on with it.
"Don't put it off because in the short term it is going to be unpopular."
Mr Clarke denied the Chancellor is "crossing his fingers", arguing that shaking up the system now is "a judgement".
He added: "I actually share George Osborne's view that this is essential if our children and our grandchildren are going to live in a successful, modern economy that is rebalanced and able to compete in the totally new world that we are beginning to face.
"If we are wrong then of course we will have to pay the price because it won't work. But meanwhile, get on with it.
"Stop looking at opinion polls and listening to the more nervous backbenchers. It is bold but I think it is necessary."