Academics' union UCU held out an 11th-hour olive branch yesterday to university bosses facing a mass marking boycott over a raid on pensions.

Lecturers and tutors at 69 sites across Britain will down pens from next week over plans to axe final-salary pensions and offer lower amounts based on "career-average" wages.

The universities of Bradford and Leeds will be the first hit on November 6 - a day before the next scheduled negotiation session between unions and employers.

Even students at the "dreaming spires" of posh Oxford and its Cambridge rival could be affected by the dispute if Universities UK (UUK) does not back down on the plans.

But UCU general secretary Sally Hunt said that the union's door remained open to increasingly isolated bosses if they were willing to meet earlier to discuss changes to the Universities Superannuation Scheme (USS) that "are full of holes."

The union's campaign against the cuts was boosted last week by major blows to UUK's argument that its proposals were the only alternative to the "unaffordable" current pension scheme.

A group of top statisticians took uni bosses to task for using "unreasonably pessimistic and incoherent" calculations and spreading "misinformation" to justify the plans.

They were based on bumper future wage rises that do not "reflect actual experience" and claims of poor returns on investments that were "difficult to understand" given the actual profits from assets racked up by the fund, said the group of mathematicians that included University of Cambridge and London School of Economics professors.

The University of Warwick - one of those facing a marking boycott - also questioned UUK's plans last week, expressing "concern" at the fact that only one option for pensions had been presented.

Ms Hunt said yesterday that members of the USS had "made it clear they are unconvinced" by the employers' arguments.

"We are being asked to buy a pig in a poke and that is simply not acceptable," she said.

"We hope the employers will come back to the table for genuine negotiations aimed at resolving the enormous gap between our two positions."