There have been sentries on campuses as university faculty begin a strike in more than 50 universities, in a dispute over pensions.
Lecturers have walked out at universities including Oxford and Cambridge at the beginning of a month-long strike campaign.
Petitions signed by 80,000 students, many backing the lecturers, are demanding refunds for lost teaching.
Universities minister Sam Gyimah has called for more negotiations.
But Mr Gyimah says students “deserve to receive the education that they are paying for. For many, this is a vital time in their studies”.
Members of the University and College Union are striking because changes to the Universities Superannuation Scheme will leave a typical lecturer almost PS10, 000 a year worse off in retirement, they say.
Younger academics could lose almost half of their total retirement income, says the union.
But the employers’ group Universities UK says the scheme has a deficit of more than PS6bn which it cannot ignore.
“This industrial action is targeted at students. It will be young people and the next generation of students who will also suffer if their education deteriorates because employers are forced to attain cuts to pay more into pensions, ” said a Universities UK spokesman.
However, there are indications that UUK may be ready to re-open talks on the issue.
UCU general secretary Sally Hunt said: “We have been calling for talks for weeks either directly or through Acas, so if UUK are willing to now meet without preconditions with a view to resolving this dispute this good news.”
Under the proposed pension plan, the USS will change from a defined benefit strategy, giving members a guaranteed income in retirement, to a defined contribution scheme, where pensions are subject to changes in the stock market.
The union says the existing scheme is performing well and UUK’s determination to push through the changes and refusal to compromise has left them no alternative but to strike.
“Staff are angry and significant disruption on campuses across the UK now seems inevitable, ” said UCU general secretary Sally Hunt.
The industrial action comes as figures suggest university bosses took home pay packages worth more than PS2 68,000 on average last year.
The Times Higher Education analysis of university fiscal accounts depicts UK vice-chancellors ensure their pay rise by only over PS10, 000 on average( 4 %) in 2016 -1 7 – nearly four times the 1.1% increase awarded to staff.
University strike: What’s it all about? Students’ compensation bid for university strike Strikes at Northern Ireland universities week one – staff at 57 universities walk out this Thursday and Friday week two – the 57 will be joined by staff at four more institutions on a three-day strike from Monday weeks three and four – staff a total of 64 universities will strike for nine days Image caption