The grades students receive for their essays are "a lottery", say researchers in a study of universities' marking standards.
Just half of tutors agreed on a mark for an essay while others took wildly different views, the researchers from North London and Surrey universities found.
Becky Francis of the Institute for Policy Studies in Education at UNL said:
"That only 50 per cent of academics could agree on the grade holds worrying implications for students and appears to lend credence to concerns that marking is an inconsistent and subjective process.
"There is a lot of divergence in the aspects of undergraduate writing that assessors value and in the marks they award to those essays. This process will be moderated by external marking, but that is usually a compromise between two marks. If students were aware of the level of subjectivity being applied, then I think they would be concerned."
With colleagues Barbara Read of UNL and Jocelyn Robson of Surrey, Dr Francis sent four essays to 100 lecturers at 24 universities - 14 were old and ten were new universities. The essays were written by students at UNL and were generally deemed worth a lower second.
But one academic thought an essay was first class while three others graded the same piece of work as third class. Likewise, five tutors awarded another essay an upper second while seven other assessors failed it outright.
The research also demonstrated that writing style is more important than content. Clear, fluid writing was by far the most frequently mentioned factor in assessing the strengths and weaknesses of the sample essays.
Tutors should discuss and practise marking sample essays with department colleagues to agree on a common approach and ensure a consistent outcome, the researchers recommend.
University Lecturers' Constructions of Undergraduate Writing funded by the Economic and Social Research Council and submitted to the British Educational Research Journal .