HERIOT-Watt University last night attempted to shoot down ''scurrilous stories'' that students received degrees with less than an aggregate of 40% in exams.

The university claimed an exclusive by The Herald's education correspondent, Carlos Alba, and follow-ups in other newspapers and television and radio were ''totally false''.

As part of its offensive, Principal John Archer sent a letter to The Herald. However, Herald editor Harry Reid said last night the paper could not publish it ''simply because it alleged that our article was defamatory''.

The Herald revealed on Thursday that students who score as little as 13% in degree exams at the university are being passed in a drive to boost the number of graduates it produces. Internal documents obtained by the paper claimed lecturers had doctored marking criteria and dumbed down classes to increase the number of students passing courses.

A confidential memo from former Principal, Professor Alistair MacFarlane, encouraged staff to take action to raise pass rates by 10%, including ''adjustment to the syllabus'' and ''modification of teaching and assessment methods''.

The professor was later warned he risked a backlash from genuinely successful students if the university was refusing to fail their less industrious counterparts.

The Herald revealed the situation dated back two years and in one department had reached ''crisis level'', according to Dr Brian Dodds, a member of the senate who has called for an independent investigation.

Last night, Mr Reid said: ''The Herald did not publish Principal Archer's letter simply because it alleged that our article was defamatory. This implied possible legal action and I am currently consulting our own legal advisers.

''The allegations that quotations in the original article by Carlos Alba were defamatory might also defame Mr Alba, who is a widely respected education correspondent in whom I have the highest confidence.

''His article was based on three documents from within the university and an official university spokesperson confirmed to us, before publication, that the documents were genuine.''

In a statement to the press and students, Professor Archer said yesterday: ''The university will vigorously defend its standards and assures all staff and students that the quality of our education is not in doubt and that an assertion that students received degrees with less than an aggregate of 40% is totally false.''

He said the stories centred around allegations from Dr Dodds, a mathematics lecturer, who had made public his opinion of assessment of modules in mathematics.

Mr Archer added: ''Dr Dodds has helped to bring the university into disrepute by refusing to dissociate himself from a totally misleading interpretation of his figures which has suggested through headlines and articles that this university virtually gives away its prestigious and hard-earned degrees.''

He said the mathematics department had totally rejected Dr Dodds's allegations of ''dumbing down'' of courses and of doctoring examination marks.

Heriot-Watt was ranked Scotland's third top university in a national survey published last week. One criteria which boosted its rating was the number of first-class degrees it conferred.

The Government plans to introduce examiners in response to an alleged blind-eye approach to failing standards under the current system of self-policed assessment. Along with six other universities in Scotland, Heriot-Watt is opposing the proposals.