Making efforts to secure better life chances for children from poorer backgrounds does not mean lowering standards, Deputy Prime Minister Nick Clegg insisted on Tuesday.
False claims of "dumbing down" are myths used by elites seeking to entrench their unwarranted privilege, he asserted in an angry attack on the status quo.
And they are the ones guilty of social engineering by protecting a system that restricts access to top universities and to the top of professions such as the judiciary.
He launched the strong defence of the Government's social mobility strategy as it published details of indicators which will be used to judge its success.
He highlighted moves to encourage universities to help state-school students by accepting lower grades from promising applicants.
"The myth is that the promotion of social mobility means lowering standards, or somehow dumbing down, to socially engineer a particular outcome," he declared.
"This is nonsense. Nonsense, I should add, which is usually peddled by those who benefit from the status quo - and therefore want to keep things the way they are.
"Social engineering is what's happening now: the unfairness in our society, and the system that perpetuates it," he will conclude in a direct swipe at critics within and outside the coalition.
"We must create a more dynamic society. One where what matters most is the person you become, not the person you were born.
"For liberals, this is core stuff. It gets to the very heart of our politics. We are a party and a creed that is defined by our belief in a fairer, more open society."
Addressing an audience at the Sutton Trust charity, he pointed out that 70% of High Court judges and 54% of bosses of FTSE 100 companies are drawn from the 7% who attend pubic school.
While one in five children are on free school meals, only one in a hundred Oxbridge entrants are.
And a fifth of those from poorer homes achieve five good GCSEs - a figure that rises to three in four among the better off, he added.
James Westhead, external relations director of charity Teach First said he welcomed the focus on social mobility.
"In too many communities in Britain, how well you do at school can be predicted by the income of your parents. It doesn’t have to be this way. We know from working in schools across seven regions in England that the quality of teaching and leadership in a school can enable children to overcome social disadvantage.
“Teachers and other professionals across the country are working to tackle this issue and improve the life chances of children from the poorest backgrounds, but more needs to be done.
“We know that no one organisation or isolated initiative can solve this problem alone because the scale of change needed is so great that it requires a movement of leaders committed to making a difference at a pupil, school and system level."
Clegg himself benefited from a public school and Oxbridge education.
But he will dismiss critics who suggest that undermines his ability to tackle the subject.
"I know some people will say I should keep quiet about social mobility, that my birth, my education and my opportunities mean I have no right to speak up," he will say.
"I couldn't disagree more. If people like me who have benefited from the system don't speak up, we will never get anywhere."
Defending attempts to widen the pool of pupils going to top universities, he said recruitment should be "on the basis of an ability to excel, not purely on previous attainment".
Opponents painted the policy as "a dangerous piece of revolutionary socialism", he will note.
But research showed state-educated pupils who achieved top A-Level grades were 50% more likely to convert that into a first-class degree than a private school pupil.
"Far from dumbing down, it's about increasing opportunity to achieve excellence. So for me this is plain common sense, and a move towards real fairness."
Clegg added that a review of social mobility, being published on Tuesday, shows "great progress" is already being made through policies such as nursery places for two year olds and the Pupil Premium
And he revealed 17 indicators which will be used to gauge their effect annually.
It comes after Labour leader Ed Miliband told the Trust the Government was taking "backward steps" on social mobility by allowing inequality to grow and denying bright youngsters from poor backgrounds the chance to succeed.
He also attacked the "snobbery" that suggests only an academic education is worthwhile, insisting that the UK must give more respect and value to vocational learning and apprenticeships.
Miliband called for a "new bargain with employers", with the Government offering the right support and incentives for them to deliver good training for long-term high-value jobs.
Deputy Prime Minister Nick Clegg, speaking on ITV's Daybreak, said: "One of the things we are doing in these figures that we are publishing today - for the first time ever, it has never been done before - we are lifting a lid, if you like, on an absolute scandal which is that, in our country more than many other countries, where you are born and certainly what your background is seems to determine your subsequent life.
"We are measuring that in lots of different ways."