Michael Gove's plans to overhaul the British education system prompted a spectacular fight with the Liberal Democrats today.
The education secretary wants to scrap GCSEs, bring back O-levels and force less talented pupils to sit simpler CSE exams, in the biggest shake-up of British education for 30 years.
"Returning to a two-tier exam system would be madness," Lib Dem president Tim Farron said.
"I say this with some bitterness and personal experience having a couple of CSE's to my name.
"By all means, lets look at the GCSE and consider reforms – Michael Gove is perfectly within his rights to do that – but lets kill off immediately any talk of returning to the divisive two-tier system that Mrs Thatcher wisely ended in the late 80s."
Dan Rogerson, co-chair of the Liberal Democrat parliamentary committee on education, said: "A two-tier system, with all the upheaval and instability this would cause, is not the way to achieve higher standards.
"Rather than harking back to an age when children started their adult life with qualifications that were seen as second rate, we want to look forward and work with teachers and schools to give them the freedom and tools needed to stretch pupils."
Liberal Democrats in the Commons Chamber made no secret of their disapproval of the plans when Mr Grove answered questions earlier today. Nick Clegg is understood to share his MPs' concerns.
The proposals, which were seen by the Daily Mail, will abolish the national curriculum and make exams significantly more difficult.
They will put Mr Gove on a collision course with teaching unions and his own civil servants as well as the Liberal Democrats.
They will not actually require any legislation and can be implemented in the next two years while preventing Labour from undoing them if it comes back to power in 2015.
The plans would end competition between exam boards, who are accused by some analysts of contributing to the dumbing down of GCSEs by making their questions easier in a bid to attract schools to their product.
Starting this autumn, exam boards will compete against each other to set the first O-levels in English, maths and the sciences, but the winner will set the exam taken nationwide.
Science will be split into physics, biology and chemistry once again, while more difficult tests will be set for subjects such as history and geography.
In maths, pupils will be expected to master challenging skills such as calculus before they can attain an A grade. In English literature, they will no longer be able to take a copy of the set text into the exam.
The requirement to obtain five A* to C grades at GCSE will be removed, but less talented pupils will take simpler CSE exams.
The plans will be announced formally in two week's time, with a public consultation in the autumn running for 12 weeks.
Labour reacted cautiously to the reports.
"Michael Gove must explain his changes to parents and pupils. Will going back to O-levels for some and CSEs for the rest really improve standards for all?" asked shadow education secretary Stephen Twigg.
"Will this divide children at fourteen into winners and losers?
"With no secondary national curriculum how will he ensure a rigorous approach to learning in all schools?"
The plans are the most radical proposals to emerge from an education secretary who has made no secret of his desire to return to an old-fashioned standard of education, with core disciplines and higher standards being reintroduced at all levels.