The Shadow Universities Secretary has denied Labour claims that the Tories would lift the cap on tuition fees if they came to power.
A Parliamentary Labour Party briefing on tuition fees seen by Times Higher Education said that the Conservatives planned to lift the fees cap.
But in his strongest statement on the subject to date, David Willetts said: "Universities have not shown that the existing tuition fee has improved students' education."
If universities wanted the cap raised, "they would need to do a much better job than they have so far of showing that fees would benefit students' experience", he added.
Asked whether the lack of evidence for educational improvement suggested that fees should not be raised, he said: "The evidence so far is very limited."
He added that a recent Universities UK report, which showed that most vice-chancellors wanted higher fees, demonstrated that the "penny has not dropped", as it failed to focus on the benefits for students.
The briefing also accused the Tories of planning to review tuition fees before evidence had been gathered, and of planning £610 million of cuts to the universities, science and skills budget.
Mr Willetts said: "It's an achievement to pack so many errors into a single sentence."