Vice-chancellors have won the first round in a continuing battle to narrow the scope of the Office for Fair Access.
Universities UK has been in extensive negotiations with ministers to define the term "underrepresented groups" used in the higher education bill, due back in the Commons for its second reading on March 31.
An early UUK briefing on the bill showed vice-chancellors to be seriously concerned that the phrasing of the bill opened them up to litigation from disgruntled students.
Higher education minister Alan Johnson has now written to the standing committee examining the bill to define the term.
The bill requires universities to present access plans to Offa showing that they have taken measures to attract applications from "groups" that are "underrepresented in higher education".
"We are fearful of being held accountable for something that is not clear and that we do not understand," said Geoffrey Copland, rector of Westminster University.
"As it currently stands, the clause is capable of mischievous interpretation," said Sir David Watson, vice-chancellor of Brighton University. "It is not sensible to have such an open-ended commitment written onto the face of the legislation. It should be part of the dialogue between Offa and the sector."
The UUK briefing also warned: "It would be completely unsatisfactory for HEIs [higher education institutions] to have to resort to litigation to find out what this phrase means.
"The best chance for scrutiny of the concept of 'underrepresented groups'
is during the passage of the bill - a chance that is wasted when powers or obligations are expressed in such vague terms and deferred until regulations are made."
After a debate in the standing committee examining the bill earlier this month, Mr Johnson said in a letter to Roger Gale, the chair of the committee, that the term "underrepresented groups" should not be "subjected to a strict statistical interpretation".
Instead, he said: "Our intention was to express in legislative terms what widening participation is about. We expect that the director (of Offa) will want to ensure that there are adequate steps taken to encourage applications from groups such as disabled students, those from lower socioeconomic groups, and those from minority ethnic groups underrepresented in higher education."
Mr Johnson also spelt out that "underrepresented groups" referred to groups underrepresented in higher education as a whole. "The success of an access plan will not be measured solely in terms of applications to the particular HEI that draws it up," he said.
However, he also warned: "This is not an excuse for failing to address particular issues in representation at individual institutions. Were such issues to arise, we would expect the university itself to have concerns, and set out proposals in its access plan to address them. I would expect that the director will take into account their proposals in determining whether or not the plan should be approved."
He also sought to clarify whether the term referred to applications or admissions. "When we talk about groups being underrepresented in higher education, we mean underrepresented in the student population. Clause 31 of the bill makes clear, however, that the action that access plans must set out will be about measures to attract applications to the institution from these groups," he said.
The Johnson letter will go some way towards placating vice-chancellors as it has some legal standing. A UUK spokesperson said: "If challenged by students, universities will at least be able to refer to this letter. But we will still be seeking further clarification as this bill goes through the Lords."
The role of Offa is expected to be a major bone of contention once the bill hits the Lords, with the Lords traditionally far more concerned than the Commons to safeguard academic freedom.
The UUK briefing said: "[The] scope of the secretary of state's powers should be reduced - does he really need power to control everything Offa does in regulations and guidance?"