This increase of 88 per cent is largely unexplained by factors that may affect attainment, the report said.
The watchdog’s chief executive warned that grade inflation remained a “significant and pressing issue” in higher education in England, as the OfS found the proportion of first class degrees being handed out has continued to rise across the years.
Around 42,000 more students graduated with firsts in summer last year compared to eight years before, according to their figures.
Concerns about grade inflation have been rife for years, amid a rising number of first-class degrees being handed out.
While the OfS found the proportion of students getting first-class degrees continued to rise, they also discovered this increase had slowed down in recent years.
Between 2017-18 and 2018-19, the proportion of firsts only rose by 0.2 percentage points, the data showed.
Nearly three-quarters of the 147 providers included in the analysis saw “unexplained” increases in first class degrees between these dates, according to the OfS analysis.
Nicola Dandridge, chief executive of the OfS, said: “This data shows that the increase in the proportion of first class degrees awarded in 2018-19 has slowed compared to previous years, with a small increase from last year in the percentage of first class degrees which cannot be explained by other factors.
“While this may indicate that the brakes have been applied, it is clear that grade inflation remains a significant and pressing issue in English higher education.”
Additional reporting by Press Association