The first university "access regulator" for England has been named.
Sir Martin promised to work as much as possible with universities
Professor Sir Martin Harris's appointment comes amid a growing row between academics and ministers over government "benchmarks" for state school intake.
Universities have said these amount to social engineering, damage their freedom and reduce the quality of higher education - and can be unfair.
But the government insists they are guidelines and not "quotas".
Sir Martin, who stepped down as vice-chancellor of Manchester University last month, will become the director of the Office for Fair Access (Offa) immediately.
Any university which wants to charge students annual tuition fees of £3,000 from 2006 will need an "access agreement" with him.
This will show their plans for bursaries for poorer students and any plans to encourage more potential students from under-represented groups to consider higher education.
He can impose sanctions - including fines - for breaches of the agreement.
The government says institutions "will set their own milestones" - separate from the benchmarks - which will "help them and Offa monitor whether their efforts to improve access are succeeding".
The benchmarks provoked a row when the annual statistics were published last month, with some universities saying theirs had been raised to unrealistic levels.
Sir Martin promised to work as "collaboratively as possible" with universities.
He added: "My past experience working in the sector has led me to understand and respect institutional autonomy and it is on this basis that I look forward to working with the sector."
On Thursday Chris Patten, chancellor of Oxford and Newcastle universities, said the benchmarks already in existence amounted to "social engineering" and undermined standards.
But the Education Secretary, Charles Clarke, said: "It is important to ensure people with talent get the opportunity to go to university if they choose to do so."
He added: "The director will not have a remit over university admissions. Admissions are and will remain a matter for universities themselves."
Professor Ivor Crewe, President of Universities UK, which represents vice-chancellors, welcomed Sir Martin's appointment, adding that much "excellent" work towards widening access was already going on.
Conservative higher education spokesman Chris Grayling said: "It is very disappointing that such an eminent figure in the university sector should accept an appointment that is so unpopular among vice-chancellors and principals.
"In order to preserve academic standards it is our clear intention to abolish Offa at the earliest opportunity and with the general election only a few months away Sir Martin's tenure is likely to be a short-lived one."
Liberal Democrat education spokesman called the regulator's post a "bureaucratic irrelevance".
He added: "Rather than a university 'access regulator' we need to ensure that the most disadvantaged children have access to quality schools."