The proportion of graduates who received firsts increased to 27 per cent last summer

Three quarters of first-class degrees awarded by some universities are unexplained, an analysis shows. Even some elite universities belonging to the Russell Group cannot justify up to a third of their firsts, the student watchdog suggests.

The disclosure comes amid growing calls for universities to reveal how they convert degree marks into firsts, to restore credibility to degree classification after rampant degree inflation, and accusations that institutions are manipulating algorithms in their favour. The proportion of firsts has increased from 8 per cent 20 years ago to 27 per cent last summer.

The Office for Students (OfS) published figures this week which showed that some universities were awarding first-class degrees to more than half of graduates. The OfS looked at the A-level results of those