Labour says it will overhaul the A-level reforms of the Michael Gove era if it wins power next year, accusing Conservatives of "turning the clock back on social mobility" as hundreds of thousands of sixth formers in England anxiously await their exam results on Thursday.

The shadow education secretary, Tristram Hunt, is poised to announce that Labour would put on hold all A-level reforms due to be introduced next year and scrap the central plan to abolish AS-levels. Gove's reforms were designed to toughen up the A-levels, moving away from coursework towards end-of-course examinations.

But the move has been deeply unpopular with university admissions officers, teachers and pupils, who complained that their subject choices were restricted. There were also claims that scrapping AS-levels disadvantaged comprehensive school pupils in university admissions because they were the most likely to make rapid progress between getting their GCSE and AS results.

Labour sources said that elements of the new A-levels would be retained, but that a delay is needed to consult and give schools the opportunity to embed the new GCSEs. The move is designed to ease the pace and scale of the reforms currently working their way through schools, which have already been warned to expect a significant dip in exam results this summer as a result of reforms to GCSEs that prevent pupils repeatedly resitting them.

"Of course we need to ensure we have rigorous assessments," Hunt will say in a major speech on Monday setting out Labour's future education policy at Microsoft's London headquarters.

"As secretary of state, I would insist on nothing less. But these changes will leave young people without the opportunity to realise their full potential. I won't allow that to happen. If I am the next education secretary, I will put a stop to it.

"The Tories are turning the clock back on social mobility. David Cameron's regressive policy to end the current AS-level qualification will close the window of opportunity for many young people wanting to go to university," Hunt will say.

"Having spoken to sixth formers across England, I know how valuable they find AS-levels in helping to shape their options and spur them on.

"Under Cameron's plan, in the future, pupils will not be open to the same opportunities as those who are receiving their exam results this week. That cannot be right."

In his speech, Hunt is also expected to attack the government's failures on teacher quality, vocational education and social mobility, while setting out Labour's agenda ahead of the election next year. The move underlines the high profile that Labour will give education in next year's general election campaign, with polling suggesting it has more public support for its handling of education policy than the coalition.

The A-level reforms were announced by Gove in 2013 and were aimed at making A-levels harder by giving pupils no option but to take a two-year-long A-level course, rather than an AS-level course as the first year of an A-level. They were due to be introduced from September 2015. But the move provoked an outcry from schools and universities that used AS-levels as part of their admissions policies.

Cambridge university said AS-levels had dramatically reduced the number of "mistakes" it made in admitting students as undergraduates, and suggested that applicants from comprehensive schools and deprived backgrounds would be more likely to miss out on places without them.

Hunt's move comes after an academic study savaged the statistics used by the DfE to justify its decision to downgrade AS-levels. The DfE had claimed AS-levels were unreliable in predicting higher education success. But a team of academics re-examined the DfE's figures and said it had crudely distorted and misapplied the data.

The researchers found that scrapping AS-levels meant that one in five students would be deprived of showing their academic improvement during their first year in sixth form, meaning that many of those capable of getting into top universities might not be given the chance. Those children are more likely to be from comprehensives than from selective and private schools.

The exam watchdog has already warned schools to expect "particularly volatile" exam results this year as a result of the reforms to GCSEs in particular. Coursework has been downgraded, with a move to more traditional end-of-course exams, and schools have been discouraged from allowing multiple resits by excluding all but the first attempt from school league tables.