Leaders of one of the world’s top universities have raised fresh concerns about the possible demise of A levels.

Richard Levin, President of Yale University, said that it would be wrong to lose the “rigour” of the exam that turns British students into world-class academics.

The depth of knowledge displayed by the best A-level students made them prime targets for America’s Ivy League universities, he said. “They are always terrific and it would be a shame to lose that rigour.”

Professor Levin’s comments, made in an interview with The Times on a brief visit to London, came days after plans were set out for diplomas that may replace A levels. He said that A-level students benefited from specialisation and were among the best prepared in the world for degree courses.

Yale, which is fourth in The Times Higher Education Supplement world university rankings, is the alma mater of the US President and his two most recent predecessors. Tony Blair’s son Euan is among 150 British post-graduate students there.

Professor Levin said the university enrolled a handful of undergraduates from Britain each year, but would like more. Yale is one of a growing number of leading US universities that mount recruiting visits to British schools. Although most entrants from Britain have been from independent schools, Yale has stepped up efforts to attract state school pupils. Of seven recruits this year, two were from state schools.

Jeffrey Brenzel, Yale’s dean of undergraduate admissions, said: “The top students from UK schools are extremely well prepared. Whereas the US system is diverse and it may be hard to evaluate the curriculum that a student has taken, one of the attractions of A level is that we feel we can rely on the results being comparable.”

The number of international students at Yale has doubled in recent years and the university is considering accommodating more. The university is one of the few in the US that offers “needs-blind” admission to all students, regardless of nationality. Those whose parental income is less than $45,000 (£22,000) a year pay no fees. Most international students receive some support. The full fee for a Yale first degree is $43,000 a year, although the university says that the true cost is twice as much.

Yale is in the middle of a four-year drive to make the university more international. Professor Levin said: “Our collaboration with British universities and academics is so long-established that our efforts are bound to be different here. We already have an exchange programme, a work internship programme and many research links.”

One important link is with the alumni who were the reason for Professor Levin’s visit. He said: “The number of Yale alumni in London has doubled in recent years because, in addition to our British graduates, many more Americans are working here.”

Professor Levin, who has been president for 14 years, was raising money not only for his internationalisation strategy, but also for an initiative to encourage leading universities across the world, including Oxford and Cambridge, to take the lead in reducing greenhouse gases.

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